Stopwatch version of FuelDump

Main features:

-time is reduced to 20 mins
-tank is 50% faster
-tank is indestructible (aka artillery is useless on it)
-main bridge is prebuilt / cannot be destroyed

etpro version uses command post as default foward spawn after tunnel doors are blown.

All other objectives / constructable are normal, although I was considering disabling the east side stage 2 defenses for the fuel depot.