Le fight club, version cflags

Last summer, I started reworking collisions in my game engine. The idea was to be able to define groups, so that e.g. collision-based communications between a stunned blador and its feet would never interfere with a bouncy branch and things it bounces away. Sure, there was way to do that already, by assigning them separate collision flags , but I've long ran out of these, forcing me to make weird…