Adds comment controller methods
* adds CommentsController#post private method which identifies the post_type
* adds CommentsController#create controller method
* adds CommentsController#comments_params method which allows mass assignment for comments
passes instance variable containing an array of answer objects for any question
adds partial pointing to new_comments form in questions list view
adds an each loop listing each comment for a question
adds answers list to questions show view, includes each questions comments, and a new comment form