QuadPlane Frame support

[iampete (Peter Hall)]

https://ardupilot.org/plane/docs/guide-tailsitter.html#quad-x-motor-tailsitter

Also worth reading the thread:

Copter Tailsitters

This topic is for discussion of development for “copter” tailsitters, which are tailsitters with multicopter motor geometries. Previous discussions took place at Dual-motor tailsitters