Topics management
remove pg
Category subscription model and migration
Fix model creation for CategorySubscription
Forum new post notification process
Merge branch 'forum-temp' into forum

Conflicts:
	db/schema.rb
Clean up buttons on topic page
Fix typo in next_unread
Force results into an array
Merge remote-tracking branch 'origin/forum' into forum

Conflicts:
	app/decorator/controllers/forem/categories_controller_decorator.rb
	app/decorator/controllers/forem/forums_controller_decorator.rb
	app/decorator/controllers/forem/topics_controller_decorator.rb