Add separate filters for operator in GamepadDriveRotationCommand.

The operator gamepad can now have its own scaling settings for robot
rotation.
Simplify the scaling code of GamepadDriveStrafeCommand.

The execute method of GamepadDriveStrafeCommand is simpler.
Move control of drivetrain reversing under GamepadDriveStrafeCommand.

The Controls class no longer handles drivetrain reversing for
GamepadDriveStrafeCommand.