raing validation error for text max length
removed title unique with project and modified queryset to check only on active story
removed title unique with project and added datamembers fields to retain list of users who have worked on a task
returning only active task list and setting them to false once a related story is deleted
added is active filters on query set and modified the error messages
Merge pull request #180 from Somesh/master

Datamodel changes for task  and added "raise validation error " in certain other scenarios