SkySurfer motor mods final version

It took some time to validate the tunings on my SkySurfer.

In particular, the Centre Of Gravity and the appropriate propeller changed a lot from the initial setup.

I therefore had to modify my files for a correct propeller folding, and to have a plane behavior unchanged whether or not I use the motor.

It resulted in a sort of tube, glued in place in the glider fuselage where the motor should stand, and 2 motor plates to choose from depending on the propeller size.

Up to 7 inches prop