adds json APIs to the forum

add this application to your forum, enable it. the following URLs/methods will now be accessible to you:

/api/category
/api/discussion (GET: id, limit, offset)
/api/discussion/add (POST:Discussion/CategoryID, Discussion/Body, Discussion/Name, Discussion/TransientKey)
/api/comment/add (POST: Comment/DiscussionID, Comment/CategoryID, Comment/Body, Comment/Name, Comment/TransientKey)
/api/session