Reintroduce stylus linting and various stylus updates/fixes

[kschiffer]

Summary

This PR reintroduces linting for our stylus files and also updates the codebase accordingly.

Changes

• Add stylelint and stylelint-stylus
• Refactor stylus codebase to adhere to new rules
• Some removal of unnecessary style definitions
• Add stylus linting to CI

Regressions

I've removed the !important flags from all utility classes. This will likely cause layout issues. However, since this PR targets the redesign branch, I believe it's a good point in time to do this since we will touch most screens anyway and can either replace or fix these issues when we see them.

Notes for Reviewers

Best to use a stylelint linting plugin for your IDEs to see this issues before pushing.
Stylelint also has a --fix flag which works quite well most of the time. In vim I use this to automatically fix issues when I save.

Checklist

• Scope: The referenced issue is addressed, there are no unrelated changes.
• Compatibility: The changes are backwards compatible with existing API, storage, configuration and CLI, according to the compatibility commitments in README.md for the chosen target branch.
• Documentation: Relevant documentation is added or updated.
• The steps/process to test this feature are clearly explained including testing for regressions.
• Changelog: Significant features, behavior changes, deprecations and fixes are added to CHANGELOG.md.
• Commits: Commit messages follow guidelines in CONTRIBUTING.md, there are no fixup commits left.

[ryaplots]

The changes look good! There's just some conflicts.