changed powertip to say 'watch #hashtag'
Made views for watching/unwatching hashtags, updated model to support watching hashtags
made watch hashtag button actually add hashtag to the user's list of watched hashtags
made custom queryset for Posts and gave it a remove_redundant method
added a watched_by filter in PostManager
added a seen_by filter in PostManager to get all posts posted, followed (user) or watched (hashtag) by a given user