Active

ticket # 31:
 apply active() to everywhere that a user sees posts. 

We'll also need to make sure status=Post.STATUSES.PUBLISHED. Also, let's combine this filter with the q_object a few lines above to reduce the chance of this:
https://docs.djangoproject.com/en/1.7/topics/db/queries/#spanning-multi-valued-relationships

By putting these criteria in seperate filter() calls, we'd end up including Tags that have unpublished Posts in viewable Channels and published Posts in Channels the user doesn't have access to. What we want is to only include published Posts in viewable Channels. Before fixing this, it would be a good idea to write a test confirming this error.

Also, let's change published__lt to published__lte here and on PostQuerySet too.