* New InstanceGroup model and associative relationship with Instances
* Associative instances between Organizations, Inventory, and Job
Templates and InstanceGroups
* Migrations for adding fields and tables for Instance Groups
* Adding activity stream reference for instance groups
* Task Manager Refactoring:
** Simplifying task manager relationships and move away from the
interstitial hash tables
** Simplify dependency determination logic
** Reduce task manager runtime complexity by removing the partial
references and moving the logic into the task manager directly or
relying on Job model logic for determinism
* First pass, adapt singleton task manager to process messages and run
jobs based on events instead of a busy loop.
* Still need to make message handing run in celery, not in a consumption
loop
