g_inactivity during warmup

[Irbyz]

g_inactivity moves players who are inactive for a certain amount of time in game to spectators.
Maybe it would make sense for it to work in warmup as well so that AFK players free up slots for people who can actually play etc.
Or maybe there could be a separate variable, e.g. g_warmupInactivity, to allow people to be inactive in warmup for longer than in game.