AntagHUD restrictions, disallow players becoming mice.

If antagHUD respawn restrictions are enabled, players will no longer be able
to use the "become mouse" verb if they have enabled their antagHUD's.

Observers were able to use antagHUD then become mice and die resetting their "has_used_antagHUD" variable allowing them to respawn bypassing the restrictions by becoming a mouse as well as respawning later.

Resolves #4300