Dual-motor tailsitters

@lorbass I’ve been testing a quadplane feature which adds manual RC control of forward throttle in VTOL modes. My results so far have been good:

although @GregCovey has run into problems (motors apparently stopping) with his Matek FC.

My mini-Convergence has the mRo X2.1 FC and my big Convergence has a Pixracer and I’ve observed no problems with them so far, with about 6 flights on the mini and ten on the bigger one.