[z2076] Move BattleGround code to separate BattleGround directory. Also some corrects to unload BG's

(based on commit [12115] - 4cfd787)
(based on commit b65bed5)
(based on commit d88a91ds)

Signed-off-by: stfx <stfx@hotmail.de>

(based on commit [s1694] - dd49d7f)