Add MF_RING Mobj Flag (Resolves #164)

This merge request creates the MF_RING flag, which unifies the logic of all ring objects, coins, spheres, ring panels, and NiGHTS stars/chips. Also in this merge request is everything from !2002, but with MF_RING used instead of MF2_FIRING. Please note I have not tested absolutely every change this merge request makes, seeing as there are alot, so please feel free to test it if you'd like.

Test exe: ringflag.exe