added rtl_yaw_final option. ch7 / yaw option YAW_RESETTOARMEDYAW changed so overridable by user

Randy
I've set the default to be, on rtl loitering above home, change yaw back to that when the quad was armed.  I think personally that is sensible and better than "no change" but you may think otherwise.  Changeable in config.h.

Thanks
Gareth