Track player count for the world and update VTR accordingly

[mibac138]

Part of #710, cc @SokyranTheDragon

[SokyranTheDragon]

All seems good. I would have perhaps preferred if the formatting changes were a separate PR, but it's a minor thing so whatever.

Also, a small thing I've noticed, branching here is no longer needed (I'll push this change in a moment):

Multiplayer/Source/Client/Patches/VTRSyncPatch.cs

Lines 46 to 49 in 94849cf

	if (__instance is Gravship or TravellingTransporters)
	__result = VTRSync.MinimumVtr;
	else
	__result = Multiplayer.AsyncWorldTime.VTR;