* Run rubocop --autocorrect on app/, config/ and lib/, also manually fix some remaining style issues
* Run rubocop --autocorrect-all on db/
* Run rubocop --autocorrect-all on `spec/` and fix remaining issues
Also add an apply_to_mentions attribute on Glitch::KeywordMute, which is
used to calculate scope. Next up: additions to the test suite to
demonstrate how scoping works.