[datalink] Fixed a bug in wifi.c

The buffer was not cleared resulting in a constant reparsing of the same message
when no other message was sent to the drone during idling time.
Big thanks to Freek for helping out with this
Enabled usage of magnetometer again and changed back SP_MAX_R to 90 deg/s
added Esky EK2-0905A joystick to play with
[conf] add ms-sidewinder joystick
[rotorcraft] big fat attempt to clean stabilization and guidance

- No more STABILIZATION_ATTITUDE_FLOAT_x in airframe file.
- Hopefully seamlessly switch between int and float.
- Also make it possible to not use a reference at all, e.g. for passthrough
[rotorcraft] remove unused STICKS_RMAT312 hack
[rotorcraft] horizontal guidance mode switching

If swtiching to HOVER or NAV mode:
reset attitude stabilization if previous mode was not using it
[rotorcraft] fix STAB_ATTITUDE telemetry
[stm32] fix init for UART6
[stm32][uart] refactor pin configuration

UART pins on F1 boards now also defined in board files
Renamed wifi to udp and started using PprzTransport again
Fixing issue that arised after commit 1de769b6f20679419e0baf41b1ab87413f7972c6, compiles fine. Test flight needed.
[mcu_periph] gpio helper functions

also removed the old gpio1 that was used on lpc and fixedwing firmware
GLS (new)

implemented a new intercept that takes into account wind on final and APP_Angle
fixed desired altitude to match the actual setpoint
should work now with any type of vertical control since all control parameters have been removed

closes #453
[conf] fix some example GLS_APPROACH defines
[stm32] spektrum for F4

Not tested on an actual F4 board!
Using some of the new gpio helper functions.
Also removed seemingly useless DebugInit.
[stm32][i2c] pin configuration in board files

Use the gpio_enable_clock helper function.
Also remove the unused scl_pin and sda_pin variables in the i2c struct.
[conf][stm32] spektrum defines for Lisa/L
[stm32][conf] fix UART1_GPIO_RX on lisa/m
[stm32] i2c3 for stm32f4, untested