Update player->quittime while a Server is Idling, Attempt 2

This is the same as !2210 (merged), but with fixed conflicts:

This merge request updates player->quittime and kicks players when their rejoin time runs out, even when a dedicated server is idling. Fixes #1119 (closed) and fixes #1143 (if the latter turns out to be a problem).

Compared to !2209 (merged), this doesn't make the server's player count go down and up when players leave and rejoin, which can be seen as either a good or a bad thing, and this fixes #1143 (again, if it is a problem). This merge request is not mutually exclusive with !2209 (merged).

TL;DR: Fixed dedicated servers not always emptying when players leave