Extracted header changes fror AP_Custom

[peterbarker]

In preparation for AP_Custom (or whatever we call it...)

Randy pointed out we should have a noun, and we had these suggestions:

AP_CustomVehicle?
AP_GenericVehicle?

I think I like AP_CustomVehicle as someone pointed out it wouldn't be a bad target for the custom build server...

Board               AP_Periph  antennatracker  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
Durandal                       *               *      *           *       *                 *      *      *
HerePro             0                                                                                     
Hitec-Airspeed      *                                                                                     
KakuteH7-bdshot                *               *      *           *       *                 *      *      *
MatekF405                      *               *      *           *       *                 *      *      *
Pixhawk1-1M-bdshot             *               *                  *       *                 *      *      *
f103-QiotekPeriph   *                                                                                     
f303-Universal      *                                                                                     
iomcu                                                                           *                         
revo-mini                      *               *      *           *       *                 *      *      *
skyviper-v2450                                                    *                                       

[rmackay9]

I'd vote for "Vehicle", "GenericVehicle", "EmptyVehicle" or "NullVehicle". I'm not a huge fan of "CustomVehicle" because nearly all AP vehicles are customised.

My favourite is just "Vehicle".

[tridge]

good to merge with minor #else change