* add new header that only contains neutrino_msg_t and friends, often this
is all that's needed instead of full rcinput.h
* directly include rcinput.h in some cpp files instead of relying on
accidental inclusion in some header
* add class forward declarations to avoid dragging in rcinput indirectly
This could use more work to further reduce the impact; maybe separating
the CRCinput::key_* constants from the rcinput class would be good.
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