Fix Safari displaying NaN for selected due date

## What does this MR do?

1. Stops using `Date.parse` to parse selected due dates. 
2. Refactors DueDateSelectors to be more maintainable and readable

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

**To review the actual fix, look here:** https://gitlab.com/gitlab-org/gitlab-ce/commit/4ad43ac3a12902d7ea01dc09f8a361b01c21a0ee. It would be difficult to pick out from the overall diff. 

## Why was this MR needed?

In Safari, the due date selector was displaying 'NaN' when a date is selected, which was being returned by `Date.parse`. Because `Date.parse` is implemented differently across browsers it's generally recommended to favor implicit Date parsing with the `Date` constructor. For more background on this, [see MDN on Date.parse](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/parse).

Also, the code for DueDateSelector was pretty messy, and its logic was very tightly coupled, so I refactored it. None of the basic logic changed, I just broke it up into smaller pieces and made it more OO. 

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22984

See merge request !6797

Fix randomly crashing spinach test for merge request

For https://gitlab.com/gitlab-org/gitlab-ce/issues/23378

See merge request !6932

Fix atom feed spinach failure

## What does this MR do?

Replaces all carriage returns in the expected commit description.

Is a partial fix to...

> spinach 5 10 https://gitlab.com/gitlab-org/gitlab-ce/builds/5132637 - partial fix in !6910

As you can see, the other half of the fix to this build is in !6910.

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

## Why was this MR needed?

Failed spinach tests

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [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
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6922

Add Pipeline metrics worker

## What does this MR do?
Creating a new Merge Request metrics is time consuming, because we need to access repository.

This makes this operation asynchronous, thus non-blocking for updating pipeline.

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

## Why was this MR needed?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [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
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6896

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Remove carriage returns from commit description as summary is on a newline and will always include carriage returns

Add RTL support to Markdown rendering

See merge request !6296

Fix trending projects Spinach failure

The trending projects list is now pre-calculated. To make this work with the Spinach test, we have to manually refresh the list.
    
Partial fix to #23378

See merge request !6911

Fix broken rspec in compare text

!6910 changed the filter text from "Filter by branch/tag" to "Filter by Git revision"

See merge request !6926

!6910 changed the filter text from "Filter by branch/tag" to "Filter by Git revision"

Fix broken Spinach tests caused by changes in !6550

!6550 added dropdowns for the branch "from" and "to" fields, but these Spinach tests were not updated accordingly.

Partial fix to #23378

See merge request !6910

Partial fix to #23378

Fix active tab test for branches page

For https://gitlab.com/gitlab-org/gitlab-ce/issues/23378

See merge request !6923

Fix Spinach merge request diff failures

gitlab-git-test `master` was updated in ff076d88, and this caused the merge request diffs to change in a way that broke assumptions in the Spinach tests.
    
Partial fix to #23378

See merge request !6916

Convert CHANGELOG to Markdown

All this does is convert the version sections into headers. The list
items shouldn't really be indented by two spaces, but it makes no
difference to the rendering and this way we retain authorship history
for the actual changes.

Related to https://gitlab.com/gitlab-org/release-tools/merge_requests/29

[ci skip]

See merge request !6925

All this does is convert the version sections into headers. The list
items shouldn't really be indented by two spaces, but it makes no
difference to the rendering and this way we retain authorship history
for the actual changes.

Related to https://gitlab.com/gitlab-org/release-tools/merge_requests/29

Add the tech writers usernames in the doc_sytleguide doc

See merge request !6924

# Conflicts:
#   doc/development/doc_styleguide.md

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix 500 error when creating mileston from group page

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/23378

See merge request !6920

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix 404 when group path has dot in the name

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/23401

See merge request !6919

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Added book club to university

## What does this MR do?

Adds the old University Book Club to the new University content

## What are the relevant issue numbers?

Closes #23353

See merge request !6888

[ci skip]

Includes a note on valid paths for cache and artifacts in the
place users are most likely to learn about the feature.

## Why was this MR needed?

We get regular support requests relating to cache and artifacts
not being picked up outside the project root. It's intended
behaviour, and should be documented.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1792

See merge request !6892

Fix Hash syntax to work for both Ruby 2.1 and 2.3

Ruby 2.1 specs were failing (e.g. https://gitlab.com/gitlab-org/gitlab-ce/builds/5149275) due the error:

```
SyntaxError: /builds/gitlab-org/gitlab-ce/app/views/devise/shared/_tabs_normal.html.haml:3: syntax error, unexpected ':', expecting =>
...'#login-pane', data: {'toggle':'tab'}, role: 'tab')).to_s));...
```

See merge request !6917

Fix broken SCSS linter errors due to missing newlines

See merge request !6918

gitlab-git-test `master` was updated in ff076d88, and this caused
the merge request diffs to change in a way that broke assumptions in the
Spinach tests.

Partial fix to #23378