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.
Use just SQL to check is a user can admin_issue on a project
Using offset pagination instead pages to avoid a count query
Tradeoff
- we duplicate how we check admin_issue in a SQL relation in the Ability class
