Use atom's language-sass grammar for SASS and SCSS

[jonmast]

Switch to using https://github.com/atom/language-sass grammars for both SASS and SCSS languages.

Description

SCCS.tmbundle is badly out of date and no longer maintained. #2965 discussed switching to a different grammar, but it was never followed through.

This PR switches to language-sass instead since it's used by both atom and vscode, and should be better maintained in the future.

Errors

There were a couple of errors associated with this change:

• The new sassdoc grammar references source.html which doesn't exist. Obviously we do have a grammar for HTML, I'm not sure if there's a way to have this use that?
• The scss grammar is now source.css.scss instead of source.css, which is included in slim. I've reversed the alias in compiler/data.go which I think should address this, but it seems like the test scripts use a docker image locally so I'm not sure how to test it.

Checklist:

• I am changing the source of a syntax highlighting grammar
  • Old: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fraw.githubusercontent.com%2FMarioRicalde%2FSCSS.tmbundle%2Fmaster%2FSyntaxes%2FSCSS.tmLanguage&grammar_text=&code_source=from-text&code_url=&code=.foo+%7B%0D%0A++%5Bbar%3D%22baz%22%5D+%7B%0D%0A++%7D%0D%0A%7D
  • New: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fraw.githubusercontent.com%2Fatom%2Flanguage-sass%2Fmaster%2Fgrammars%2Fscss.cson&grammar_text=&code_source=from-text&code_url=&code=.foo+%7B%0D%0A++%5Bbar%3D%22baz%22%5D+%7B%0D%0A++%7D%0D%0A%7D

[jonmast]

Looks like CI is failing due to the license. It looks like it's just two MIT licenses concatenated together, but it gets detected as "other".

Manual license override has been done.

[Alhadis]

Good idea.