Improve note validation

This MR improves note validation. Originates from #15577.

Closes #17260

See merge request !4024

❤

Use absolute paths in .gitignore

See merge request !4335

It's working fine now but by making it more explicit we can make tools
like 'The Silver Searcher' to parse properly the .gitignore file

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/15577

Use $ as the snippet prefix so it's consistent

## What does this MR do?

Change like `Snippet #20073` to `Snippet $20073`

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

Are there any other places need this change?

See merge request !4338

Project#show on projects pending deletion will 404

fixes #17508

See merge request !4156

fixes #17508

Fix import URL migration error

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/17956

See merge request !4321

Update notes immediately after closing/reopening

## What does this MR do?
Fixes MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4127 Thanks @bendyorke!
## Are there points in the code the reviewer needs to double check?
Nope.
## Why was this MR needed?
Constant conflicts in that MR
## What are the relevant issue numbers?

## Screenshots (if relevant)

Fixes #15091 

See merge request !4323

Fixed issue with calendar activity button not sending request correctly

When you click on a square it now sends the AJAX to the correct URL rather than the current URL. This was causing an issue where it would be loading the same page & inserting that into the DOM, rather than calendar activity events.

See merge request !4322

Fixed issue with spacing in issuable header

## What does this MR do?

Fixes an issue with spacing next to the word 'by' in the issuable header

## What are the relevant issue numbers?

Closes #17864 

## Screenshots (if relevant)

![Screen_Shot_2016-05-27_at_11.53.37](/uploads/464c2149df304109726b7d7ab855ebe1/Screen_Shot_2016-05-27_at_11.53.37.png)

See merge request !4314

Use gitlab-workhorse 0.7.4

See merge request !4317

Changelog entry for queue duration

See merge request !4316

Fixed potential issue with 2 ci status polling events happening

Possible cause for double notifications was if the request was slow & then you changed page whilst this request was happening it would finish on another page & then launch another interval - this stops that issue.

Also passed in the CI status as an option value rather than waiting for the first ajax request to finish

See merge request !3869

This enables
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4278 .