Fix subscriptions:clear task, refactor feeds, refactor streamable activites

and atom feed generation to some extent, as well as the way mentions are
stored

app/models/favourite.rb

@@ -1,9 +1,9 @@
 class Favourite < ActiveRecord::Base
+  include Streamable
+
   belongs_to :account, inverse_of: :favourites
   belongs_to :status,  inverse_of: :favourites
 
-  has_one :stream_entry, as: :activity
-
   def verb
     :favorite
   end
@@ -12,27 +12,15 @@ class Favourite < ActiveRecord::Base
     "#{self.account.acct} favourited a status by #{self.status.account.acct}"
   end
 
-  def content
-    title
-  end
-
   def object_type
     target.object_type
   end
 
-  def target
+  def thread
     self.status
   end
 
-  def mentions
-    []
-  end
-
-  def thread
-    target
-  end
-
-  after_create do
-    self.account.stream_entries.create!(activity: self)
+  def target
+    thread
   end
 end