Upgrade eslint 3 -> 4

What does this MR do?

Update eslint 3 to eslint 4.

Changed rules:

Type	Rule	TL;DR
➕	prefer-promise-reject-errors	Promises should be rejected with an error (e.g. Promise.reject(new Error(msg)) rather than Promise.reject(msg)
➕	no-await-in-loop	Don't use await in loop bodies, push to an array and use await Promise.all(arr)
➕	no-return-assign	No return foo = bar + 2 allowed anymore
➕	for-direction	For loops only allowed in positive direction (i++ and no i--)
➕	getter-return	Custom getters now need to return something
➕	no-compare-neg-zero	Do not compare to -0
➕	semi-style	Semi-colons are now enforced at the end of the line
➕	no-buffer-constructor	Node specific, but no new Buffer
➕	switch-colon-spacing	case 'x': console.log('Success'): Ensure that colon has no space before, but one space after case statements
➕	template-tag-spacing	Tagged template literals are not allowed to have spaces before them. As we do not make use of them, not that big of a deal
📝	no-unused-vars	ignoreRestSiblings is now set, which means that const {var1, ...unusedRest} is fine now
📝	no-param-reassign	Is now allowed for some objects, e.g. res.data = 'foo' is fine now
➖	no-duplicate-imports	import/no-duplicates is used instead

Caveats

The following rules have been disabled (for now?), as they require too many changes:

• prefer-destructuring
• no-restricted-globals
• no-multi-assign
• We are using the old indent-legacy instead of the improved indent for now.

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

• The removal of the unused createComponentWithMixin: 9a9f758d

Does this MR meet the acceptance criteria?

• [n/a] Changelog entry added, if necessary
• [n/a] Documentation created/updated
• [n/a] API support added
• [n/a] Tests added for this feature/bug
• Conform by the code review guidelines
  • [n/a] Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • [n/a] Has been reviewed by a Backend maintainer
  • [n/a] Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes: https://gitlab.com/gitlab-org/gitlab-ce/issues/40476