Fixed some bugs in tasks, apple feature:

* Update ordergroup stats when task is destroyed.
* Removed assigned caching attribute in task object.
* A lot of eager loading for tasks controller.

app/models/assignment.rb

@@ -2,16 +2,6 @@ class Assignment < ActiveRecord::Base
   
   belongs_to :user
   belongs_to :task
-  
-  # after user is assigned mark task as assigned
-  def after_create
-      self.task.update_attribute(:assigned, true)
-  end
-  
-  # update assigned-attribute
-  def after_destroy
-    self.task.update_attribute(:assigned, false) if self.task.assignments.empty?
-  end
 end