Made the search bar on emoji menu sticky
## What does this MR do?
When scrolling down the emoji menu, the search bar disappears. For better UX, the search bar no stays at the top when scrolling.
## Screenshots (if relevant)

See merge request !4743
Rename Code tab to Repository
As discussed in #18830, this renames the "Code" tab to "Repository".
Screenshot now:

See merge request !4807
+ Move 'Edit Project/Group' out of membership-related partial
+ Show the access request buttons only to logged-in users
+ Put the request access buttons out of in a more visible button
+ Improve the copy in the #remove_member_message helper
Signed-off-by: Rémy Coutable <remy@rymai.me>
Fix wiki linking behavior for markdown wiki pages
Related to #18019
- As per the documentation in !4372
## TODO
- [ ] !4432 Have wiki linking behave as per the documentation
- [x] Move `WikiLinkFilter` specs to the pipeline level
- [x] Verify current behavior on wiki `show` page
- [x] Fix current behavior on wiki `show` page
- [x] Verify current behaviour on wiki preview
- [x] Fix current behaviour on wiki preview
- [x] Rewrite all links and get preview links working
- [x] Make sure all links are on-par with the wiki `show` page
- [x] TDD `WikiLinkFilter` and get it working
- [x] Hook `WikiLinkFilter` up
- [x] Fix tests
- [x] Fix `markdown_spec`
- [x] Fix `wiki` spinach feature
- [x] Wait for [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/4f50dd2/builds) to pass
- [x] Make sure all wiki-related pages are working as expected (history, all pages, etc.)
- [x] Test in different ruby versions
- [x] GitLab instances hosted on a relative URL
- [x] Non-markdown rendering formats?
- [x] RDoc
- [x] ASCIIDoc
- [x] Create issues to fix things for RDoc and ASCIIDoc
- [x] Gauge performance impact
- [x] Refactor
- [x] Re-organize commits
- [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/f860e9a8dcabe7d5f160c32fc549807c98baa4a1/builds) passes
- [x] Respond to @rymai's comments
- [x] `class WikiLinkFilter < HTML::Pipeline::Filter`
- [x] blank line after guard clause
- [x] keyword arguments for `wiki` and `slug`
- [x] invert the condition
- [x] inline `user` in spec
- [x] Make sure spec names are not out of date
- [x] Comment for each rewrite rule
- [x] Add CHANGELOG entry
- [x] Reorganize commits
- [x] Make sure [build](https://gitlab.com/gitlab-org/gitlab-ce/commit/19b91e749a6320d12fb299d33f1f6440777e0e26/builds) passes
- [ ] Wait for merge
See merge request !4432
- Need to pass in a `page_slug` to the filter, so it can rewrite based
on the current page (all links are rewritten to the level of the app root).
- The earlier `markdown_preview` endpoint was at the level of the wiki.
We need to know the current page (for rewriting, as above), so this
commit moves the endpoint to the level of a wiki page.
- Fix all tests
Notifications dropdown on project page now has descriptions
## What does this MR do?
Adds descriptions to the notification settings dropdown on project pages. Also changed the order of them to make more sense.
## What are the relevant issue numbers?
Part of #12758
## Screenshots (if relevant)

See merge request !4374
Fix grammar and wording in text on various pages.
## What does this MR do?
Fixes various grammatical and/or wording issues I found while copyediting on the plane :)
## Why was this MR needed?
Incorrect grammar and weird/confusing wording makes the product look less polished and professional.
See merge request !4237