Merge branch 'master' into glitch-soc/tentative-merge

Conflicts:
	README.md
	app/controllers/statuses_controller.rb
	app/lib/feed_manager.rb
	config/navigation.rb
	spec/lib/feed_manager_spec.rb

Conflicts were resolved by taking both versions for each change.
This means the two filter systems (glitch-soc's keyword mutes and tootsuite's
custom filters) are in place, which will be changed in a follow-up commit.

app/serializers/rest/filter_serializer.rb

@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class REST::FilterSerializer < ActiveModel::Serializer
+  attributes :id, :phrase, :context, :whole_word, :expires_at,
+             :irreversible
+end