Add Cube controller events

Refactor code:

* Add Cube Registry to keep track of configured cubes
* Add Cube object for interactions with a single Docker Container
* Split between Observing Container lifecycles, executing Controller
events and Object creation

fixes #19
fixup! Add Cube controller events
fixup! Add Cube controller events
Merge pull request #24 from aslakknutsen/command_events

Add Cube controller events