Add support for switching round gamemodes at the start of the round.
The Round starts with an "unassigned" gamemode. The gamemode is selected after a few seconds.
The round gamemode (zsb_roundgamemode) can also be switched in the middle of a round, and the game will do its best to alter player loadouts and such to fit the new gamemode.
Replaced the old, convoluted round gamemode selection logic with a simple cycle (transmission, then collection, then deathmatch, repeat.)
Add support for switching round gamemodes at the start of the round.