Implementing models for instance groups, updating task manager

* 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

tools/docker-compose.yml

@@ -33,7 +33,7 @@ services:
       dockerfile: Dockerfile-logstash
   # Postgres Database Container
   postgres:
-    image: postgres:9.4.1
+    image: postgres:9.6
   memcached:
     image: memcached:alpine
     ports: