Most of the MotorSafety implementation was moved into the MotorSafety base
class. SafePWM's inheritance of MotorSafety was moved into PWM to
eliminate Java needing a helper class.
In Java, a helper class for Sendable (SendableImpl) was added due to
lack of multiple inheritance.
SendableBuilder.setActuator() sets the .actuator key in the network table
so dashboards can change behavior on the client side if desired, and also
sets a local flag (retrievable via isActuator()).
Both make drive bases actuators and call setSafeState on them.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
