Update mw.c

Altered and stripped down Gtune just for the P parts(Roll / Pitch / Yaw) and with +-50% authority concerning the preset Ps. http://diydrones.com/profiles/blogs/zero-pid-tunes-for-multirotors-part-2 describes the basic function however this is not zero pid! You start normally then put your copter in acro if it isn't already and then engage gtune and keep your fingers crossed that your copter won't crash... Values are normally not saved so check in gui the gathered P values while still powered. Fiddeling on the sticks will not harm but tuning the corresponding axis is stopped till you center that stick again. TRY AT YOUR VERY OWN RISK (1m above HIGH grass or so)