[12676] All units can have Not_Selectable flag while boarded on vehicle

Thanks to debilvul for pointing
[12677] Make use of GROUP_UPDATE_FLAG_VEHICLE_SEAT

Original patch by thenecromancer (TC)
[12678] Fix possible client crash when passenger despawns while boarded
[12679] Revert [12646]. This needs to be fixed in another way!

Close scriptdev2/scriptdev2#113
[12680] Improve [12678] with additional Vehicle checkes

This is required because transports are not always vehicles
[12681] Fix spell 9712

Fix player spell 9712 used in quests 2203 & 2501. Spell 9712 has NPC target while triggered spell 21029 has self-target (player).

Signed-off-by: Cala Haryon <calaftp@free.fr>
[12682] Disable AI attack for controllable vehicles

This won't allow vehicles which can be controlled to use any type of AI attack