build: split up the build system to allow for better board support

this will make it easier to support boards like the VRBrain
build: fixed eclipse build on Windows for PX4
Rover: change PX4 main baud rate back to 115200

we now use USB console
Copter: change PX4 main baud rate back to 115200
    
we now use USB console
Rover: removed obsolete files
Rover: default magnetometer to enabled

will be disabled by auto-detect code if not attached
Rover: don't override declination on startup
Rover: fixed comments
Rover: added 'level' CLI and reboot command
Rover: tweaked parameters and added SPEED_TURN_GAIN and SPEED_TURN_DIST
Plane: update SERIAL0_BAUD parameter description
HAL_AVR: expand analog input test to more channels
HAL_AVR: fixed analog input with high channel numbers
AP_HAL: moved AnalogIn example to generic examples

it is not AVR specific anymore
AC : global static variables should not be initialized to zero
Copter: increase low voltage check to 10.5v

Change requested by Rob Lefebvre and Richie Wilson
AC: Flip code fix

Flight tested it today and made some flips. Throttle adjusted in Manual throttle modes. Not tested in AP throttle modes such as alt hold.
AC: Moving flip speed back to 400°/s to prevent oscillation around change in speed.

Would like to add a more gradual speed change in the finish. Might require a new state as the copter passes -90°
AP_HAL_PX4: fix off-by-one error in RCOutput channel sending
Copter: inertial nav waypoint controller

#define added to allow compile time selection of traditional or inav
based loiter and wp controllers