Task refactoring

I'm pushing this branch as a merge request to make it easier to gather feedback/reviews/tests from other contributors (like @peb-guest). I have spent a lots of time on designing and implementing this new task framework. It passes all unit tests and the tasks seem to be running.

Please try out this code and report back your results (both good and bad). And don't hesitate to review the code if you want (but it's a significant amount of code).