Added tuning mode logic to allow for pid tuning or yaw hold in velocity mode

Created parameter to allow users to either be in tuning mode or not. When not in tuning mode the yaw holds its current yaw when yaw rate it 0. When yaw rate is non-zero, moves the yaw angle setpoint like a moving target.

When tuning mode is on, the yaw rate directly controls the yaw rate of the controller similar to the other axes. This is required to tune the yaw rate pid.

This allows users to switch between pid tuning mode and flying mode on the fly.