TRX-4 forward servo mount

Front servo mount for the Traxxas TRX4 (-kit or any other with inner fenders).
(For the "Sport"-variant see thing #5673754).
It replaces the original front battery support (8223) and the original servo mount (8239),
so it is meant to be for steering only, not for servo winches.

Good reasons for reloacating the servo are:
- more forward weight,
- prevent collision of servo horn to panhard rod at full droop,
- create more space for bigger or forward mounted motors,
- create space for front longitudinal mounted battery pack.

This servo mount was designed for either the original Traxxas servo (2075X),
or slightly lager ones like the Power HD LW25MG in particular.
As I use the Traxxas metal servo horn (8247X), the servo sits as low as possible.
That said, the use of other servo horns would require the servo to sit higher,
so it does not collide with the lower steering rod.

So if you don't use either the original or the metal servo horn from Traxxas,
choose the "+3mm_