Some fixes for projects migrations
Created abstract BaseTask model + default implementation
Edited the migration files to make them point at the right models at 'all times' (if you don't fiddle with settings between migrations)
Cleaning up some unused imports, replaced direct Task model references with get_task_model
Added db_table statements to migrations
Started with fixing tests
Merge pull request #134 from sergei-maertens/abstract-task

Abstract task