Converted replies from custom comments to custom posts

Also changed the usage of word comment/comments with reply/replies
Using get_the_date/get_the_time instead of mysql2date/mysql2time
Using WP_Query class to get replies count instead of querying db directly
Setting `supports` as false instead of an empty array to make code look better
Merge pull request #90 from VarunAgw/post-table

Converted replies from being stored as comments to being stored as `sf_thread` posts.