removed Task object awareness from TaskCell.
removed all domain related data from the TaskCell
edited to reflect changes to TaskCell. Added a method to set the TaskCell as active
added images back. remove methods for setting the cell active/inactive and placed all cell configuration under a setup method
fixed single task completion and all tasks completion.
completing a task now makes all child tasks complete as well.
made some of the properties private
made childreTasks readonly. Added a hasChildren method to the Task class