Adds blog.tags extension to update tags 
Adds callback method that gets called right before Blog object gets deleted to make sure that tags that will be empty once the object gets deleted will be deleted.
Sets default values to the order of blogs and comments
Adds #update action
Adds method that permits params[:blog] attributes to avoid csrf error.
Adds Some helper private methods
Adds blog editing functionality to the app.
BlogListController passes the blog begin updated to the BlogFormCotnroller using $broadcast. And the rest of the work is done by BlogFormController. 
Once the update is done on the server side, the blog Factory uses promise to let the BFCtrl know the the blog was successfully updated.
Refactor: naming changes to functions for readability