Remove flight_mixer.c's dependency on mw.h/board.h.

This is a large commit, from the commit it is clear that the mixer has
many dependencies, this is expected since it is central to the
application.

To achieve the decoupling many master config and profile members had to
be moved into structures.

Relocated throttle/pitch curves into rc_curves.c/h since it has nothing
to with rx code, this fixed the dependencies inside the rx provider
files.