Method: Prefetch actors of activities and cache them.
Method: Pre fetch comments of activities and cache them.
Method: Check if current activity have group.
Method: Start group.
Method: End group loop.
Method: Get activity by activity_id.
Method: Delete single and multiple activity from database.
Method: Initialize the activity class.
Method: Prepare and fetch notifications from database.
Method: Prepare all actions of activity. Numeric keys are used here so that we can save space while saving in database.
