Spawn blood splats

For each MT_BLOOD, spawn an MT_BLOODSPLAT in one of 8 random states on
the floor. These MT_BLOODSPLATs inherit any color change from MT_BLOOD,
will stay for 10 minutes, and won't appear as thing triangles in the
automap.
MF_BLOCKMAP has also been removed from MT_BLOOD so it will rise or fall
if sector height changes.