Content Security Policy

Ref: #18231 

This uses twitter's [secure_headers gem](https://github.com/twitter/secureheaders).

See merge request !4770

Collapsed diffs lines/size don't accumulate to overflow diffs.

## What does this MR do?

Reduce the number of lines that we highlight on big diffs to try to reduce the degradation introduced by  !4990 as you can see on the issue description #19820 .

We collapse any files after the diff is over the number of safe files (100), or over the safe lines (500) or over the safe number of bytes (5KB x 100 files).

We still need to bump the gitlab_git and point this branch to the new gitlab_git version.

## What are the relevant issue numbers?

Closes #19820 
Closes #19885

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- ~~[ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~[ ] API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5306

Render only commit title

## What does this MR do?
Render only commit title in builds



## Why was this MR needed?
Better readability

## What are the relevant issue numbers?
Closes #19420 

## Screenshots (if relevant)
![after](/uploads/fcdd59d74a0f91f6ac847f7f02d5f07f/after.png)![before](/uploads/71ca6dabf31452a1a8dfb15ecb8860c5/before.png)
## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added


- Tests

- [x] All builds are passing
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc: @kradydal @yorickpeterse @grzesiek @tmaczukin @dzaporozhets [@tomash](https://github.com/tomash) [@chastell](https://github.com/chastell)

this is connected to closed MR [!5109](https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5109)

See merge request !5131

Gravatar, Google Analytics, Piwik, Recaptcha, etc.

Improve markdown

Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4975 (thanks @sheerun) with small changes on top

cc @iamphill @tauriedavis 

See merge request !5314

Revert "Revert "Merge branch '18193-developers-can-merge' into 'master'""

## What does this MR do?

Reverts the revert of !4892 which lacked an EE MR at the time. This has been done in gitlab-org/gitlab-ee!564.

## What are the relevant issue numbers?

Closes #19872.

See merge request !5310

Fix activity heatmap to show proper day name.

## What does this MR do?
This MR fixes issue #19909.

## Are there points in the code the reviewer needs to double check?
Not necessarily, it's pretty straightforward, buuuut

There was some discussion about whether GL wanted the activity heatmap to start on Monday or Sunday, this fix makes it start on Sunday, if GL is wanting it to start on Monday then some more substantial changes need to be made on the `calendar.js.coffee` script.

## Why was this MR needed?
The amount of day names that were off from their dates was too damn high! :P 

## What are the relevant issue numbers?
Directly #19909 

Also some related discussion (feature discussion):
#19282, #5988

## Screenshots (if relevant)
**Currently on GL.com**
![Screen_Shot_2016-07-16_at_10.56.02_PM](/uploads/b45cfc56c29a8865a2bdc1f798409706/Screen_Shot_2016-07-16_at_10.56.02_PM.png)

**After MR**
![Screen_Shot_2016-07-16_at_10.56.30_PM](/uploads/d8655bb259ced443a2c572ff03dcb8bb/Screen_Shot_2016-07-16_at_10.56.30_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5303

Don't blow up in tree view on empty repo

## What does this MR do?

Stop the empty repo page blowing up with a 500 error when a user's default view is tree view.

## Are there points in the code the reviewer needs to double check?

Don't think so.

## Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4997 made sure that the `tree` filter was only called if the user's default project view is tree, but left out the empty repo check. When users visit an empty repo with the tree view as default, they now get a 500.

## What are the relevant issue numbers?

Closes #19928.

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~ (bug introduced in same release)
- ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- ~~API support added~~
- Tests
  - ~~Added for this feature/bug~~
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5317

Don't parse Rinku returned value to DocFragment when didn't change original html string.

See merge request !5311

- This was introduced (at some point) while rebasing `master` against
  the "developers can merge" feature branch.

- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5310#note_13139705

add modification to commit title test

add empty line

Disable transaction when adding index for Ci::Pipeline

## What does this MR do?
Adds missing `disable_ddl_transaction!`

## Why was this MR needed?
Fixes a broken migration for PostgreSQL


See merge request !5319

Store when and yaml variables in builds table

## What does this MR do?
Stores `when` and `yaml_variables` in `ci_builds` table.

## Why was this MR needed?
This is done in order to simplify the code responsible for creating a pipeline builds.

## What are the relevant issue numbers?
This made as a pre-step for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5295.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5296

modify view test to commit title-repair rubocop

modify view test to commit title-repair rubocop

modify view test to commit title-repair rubocop

remove empty line in CHANGELOG

repair rubocop test and update CHANGELOG

repair rubocop test

repair rubocop

repair rubocop

repair rubocop

update CHANGELOG

modify view test to commit title-repair rubocop

modify view test to commit title-repair rubocop

modify view test to commit title-repair rubocop

repair rubocop test and update CHANGELOG

repair rubocop test

repair rubocop

repair rubocop

repair rubocop

add git-commit-title-method into tests