Door::Visible: don't treat doors with the iwd2 hidden bit set as visible

i hope the other games don't have garbage in the high bits
GameControl::Draw: don't highlight HIDDEN doors
TileMap::GetDoor(const Point &p): ignore HIDDEN doors

fixes the wrong door being used for overDoor when a hidden door is
 overlapping another one (eg. for Tabbard's shield)
GameScript::SetDoorFlag: removed hack from 56dc6ec0587f for iwd2 ar1200

tabbard's shield is now properly accessible since the previous commit
 and now also the elaborate rock pile traps in ar4100 toggle properly
gemrb_ini.txt: document MeleeHeaderUsesProjectile