Improved unit tests in 'test_clerk'.
Improved encapsulation of state variables.
Added 'applyTorqueAndForce' function to Bullet and its Cython interface.
Internally Azrael now only uses central forces and torques instead of
non-central forces.
Implemented control commands for Boosters and Factories.
Cleanup: changed several variable names.
Removed default arguments from 'parts.Boosters'.
Tests do not spawn superflous controller processes anymore.
TLC and PEP8
Codec for controlParts functions now serialise factory commands.
Added 'sendControl' function to controller interface.
bugfix: factories now spawn objects with correct orientation.
Start script now adds a complex object with two boosters and two factories to
the simulation.
Player does not rendered anymore on its own screen.
Modified the demo controller to send command to its parts instead of using the
low level setForce function.
'controlParts' method only updates force and torque if at least one booster
command was supplied.
WSControllerBase can now attach to an existing object.
PEP8