Create ActorSystem for saner encapsulation of all global structures

This currently contains all of the global structures in one place. 
See the [Trello](https://trello.com/c/XfCcOGyk) for more info. 

I have moved the supervision so that actors are added underneath a root supervisor which I will remove before merging. 

Ideally we will make our test suite more modular and less dependent on globals unless directly testing that API.