* Changed `traps_setting` config values.
* 0 = Always visible (default)
* 1 = Enable invisibility in versus maps (GVG/PVP/BG)
* 2 = Enable invisibility in all maps
* Added skill unit flag `UF_HIDDEN_TRAP 0x20000` for trap invisibilty.
NOTES:
* Invisible traps are always visible for the trapper and trapper's partymates.
* If the trap is invisible, it always be hid immediately (except the people above).
* Revealed hidden traps, are always visible by everyone.
* Currently, only `HT_DETECTING` that can reveal the hidden traps (hardcoded). TODO: Sight, Ruwach, and Improve Concentration also able to reveal hidden traps.
Signed-off-by: Cydh Ramdh <cydh@pservero.com>