PHPBB3-14865 Use Stylelint for managing css standards

[hanakin]

We need to allow for better control over the state of our css via linting.

I am recommending we use

http://stylelint.io/

It provides the best control over everything we would want to manage. It expands on our currently rudimentary and all beit possibly archaic front-end standards

Best of all it provides us a manner in which to easily test for our standards without tedious manual review

The standards I have set are loosly based on http://cssguidelin.es/

Tracker: https://tracker.phpbb.com/browse/PHPBB3-14865
PR: https://github.com/phpbb/phpbb/pull/4509

[Marc]

Sounds good to me. I'm happy to use any tools that help improving our code quality no matter what type it is.

[3Di]

+ 1