There was a lot of duplicated code between all 7 PWM speed controllers.
This moves all the duplicated code down to a base class, that will make
it easier to add speed controllers in future years if needed again. Also
if we need to add a method to all speed controllers, we only have to do
it in 1 place, and not 7.
Change-Id: I25eb1d097c0f5f7dbd7656db2f4a30d006d50f98
