* master: (389 commits)
Document "No gems fetched from git repositories" policy [ci skip]
Typos
Small gramatical tweaks
Typos
Added PHP & NPM doc
Use `:empty_project` where possible in request specs
Add caching of droplab ajax requests
Use `:empty_project` where possible in model specs
Revert 3f17f29a
Remove unused js response from refs controller
Add MR id to changelog entry
fixed small mini pipeline graph line glitch
Prevent form to be submitted twice
Fix Error 500 when repositories contain annotated tags pointing to blobs
Fix /explore sorting (trending)
Simplify wording in "adding an image" docs
Remove "official merge window" from CONTRIBUTING.md [ci skip]
Update repository check documentation
Fixed flexbox and wrap issues
Update two_factor_authentication.md
...
Add ESLint
## What does this MR do?
- create `package.json`
- add ESLint dependencies to `package.json`
- add JavaScript linting to CI
- add Rake task `lint:javascript`as alias for `eslint` (which itself is an alias for `npm run eslint`)
## Are there points in the code the reviewer needs to double check?
Probably not.
## Why was this MR needed?
My hovercraft was full of eels.
## What are the relevant issue numbers?
- https://gitlab.com/gitlab-org/gitlab-ce/issues/13224#note_12537431
- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5006#note_13255658
See merge request !5445
CoffeeScript generated JavaScript contains some unreadable
expressions. This refactoring addresses complex uses of
the exestential operator that produced unreadable Javascript.
