Add ActionManager methods to get streams for particular objects
Add ActionManager methods to get streams for particular objects

* stream_form_object: stream of actions where the object (instance) is either the
  action_object or taget_object of the action
* stream_for_object_as_object: stream of actions where the object (instance) is the
  action_object of the action
* stream_for_object_as_target: stream of actions where the object (instance) is the
  target_object of the action

affan2/django-activity-stream,JeromeParadis/django-activity-stream,pknowles/django-activity-stream,Shanto/django-activity-stream,druss16/danslist,thelabnyc/django-activity-stream,JeromeParadis/django-activity-stream,Eksmo/django-activity-stream,azizmb/django-activity-stream,druss16/danslist,thelabnyc/django-activity-stream,pombredanne/django-activity-stream,jrsupplee/django-activity-stream,jimlyndon/django-activity-stream,justquick/django-activity-stream,hiepthai/django-activity-stream,affan2/django-activity-stream,hiepthai/django-activity-stream,Shanto/django-activity-stream,azizmb/django-activity-stream,jrsupplee/django-activity-stream,justquick/django-activity-stream,druss16/danslist,intelivix/django-activity-stream,pknowles/django-activity-stream,pombredanne/django-activity-stream,github-account-because-they-want-it/django-activity-stream,intelivix/django-activity-stream,Eksmo/django-activity-stream,jimlyndon/django-activity-stream,github-account-because-they-want-it/django-activity-stream