Almost there

Got the bulk of the "RigidPanel" code moved over as a parallel implementation of the ultipanel.  Because IAP's panel is a "hardware fork" we probably don't need to worry about keeping the code in the same file as the ultipanel -- evolution of the two products aren't likely to be directly applicable to each other.  We still need some Makefile cleanup to make the RigidPanel an "option" and then testing all of this on various RigidBot configs.  Otherwise there is no more code in the InventAPart/RigidBot-Firmware repo to bring over!