Create comment partial, migrate db, update models
Make comments on posts polymorphic

-make comments polymorphic
-make replies controller for comments that reply to other comments
-make new routes for comments and replies
Make replies#create, display comments in nested lists
Refactor replies controller into comments controller
Add permalinks to comments partial
Make comment#create redirect to parent anchor
User can add categories to posts
Add categories to posts
Switch category dropdown to use title not name