Further SCSS linting additions

I'm adding stylelint and stylelint-scss rules right now, and some possibilities might be nice but will require more work to be possible. This is to keep to keep track of those in case I want to do the work sometime in the future.

• Some of the selector limitations could be useful to reduce complexity, but probably a lot of violations existing: https://stylelint.io/user-guide/rules/#selector-1
• selector-no-qualifying-type specifically is probably doable, but will need some changes.
• no-descending-specificity - could be indicating existing issues, there are a lot of violations though
• max-nesting-depth could probably be set to 2, but will need a few fixes
• scss/selector-nest-combinators - might be nice, makes the rules more consistently readable but there are a lot of violations currently.