Unit, System Tests for bluesky code

[reube]

Produce framework for unit, system tests, regarding

1. updates made to the overall model as a result of input commands,
2. model updates based on the passage of time.

Definition of done:

• Framework established - simple task
• Establish the target modules for testing - for system tests this means establishing key flows through the code that should be stressed.

(See opening paragraph of https://github.com/ethertricity/bluesky/wiki/Code-Summary - there is a single main loop which does these two kinds of model updates).
Should start simple by focusing on the autopilot (bluesky.traf.autopilot.Autopilot) and flight path (bluesky.traf.traffic.Traffic) models.