Add dogtag/bodybag based respawn system #161

If a player dies, his dogtag/bodybag must be recovered (and optionally transported to base/wherever) to allow him to respawn according to the rest of the respawn rules. E.g. if respawn is controlled by events only, then it should check which players can be respawned when event is raised. This allows compatibility with respawn after task scheme and even more.

This would make retrieving dogtags and bodies useful, which might be beneficial for some more serious or long scenarios.