It's been requested by a few different people that we backport the eslint to earlier branches.

I don't think we should do a straight backport though cos:

• Adding eslint into the grunt toolchain is a nono - we can't break peoples production builds
• The eslint version in master requires node 4, we can't raise that on stables either

So instead I propose:

• We backport the config file
• We add a package.json entry for eslint so its installed with npm
• We backport the eslint ignore/global definitions comments to reduce noise

There will still be a lot of complaints in existing code but:
https://docs.moodle.org/dev/Coding_Style#Policy_about_coding-style_only_fixes