Fixed|All Games: Latent links to deceased mobjs in the Blockmap

Whenever a mobj is moved on the XY plane, regardless of the distance,
it is paramount that the engine is informed of the move. This means
calling P_MobjUnlink() beforehand, then adjusting the origin and then
finalizing the move by calling P_MobjLink().
Server: Removed gridmap.h/cpp from the project