Simplify motors

I am quite happy with the base module which is cleaner and provides only 4 public classes now without any mixins.
On the other hand the dummy motors are still quite weird but work thanks to the C3 linearization rule and the fact that I added manual invocation of mixin constructors which is not so nice but allows us not to repeat ourselves... The user doesn't really need to understand how and why it does work, the question is if we will understand it couple of moths from now :smile: