AI: make asw_pathfinder_npc invisible

asw_pathfinder_npc is spawned at (0, 0, 0) when the AI director is
looking for a place to spawn a horde. In some maps, the location (0, 0,
0) is visible.

Fun fact: asw_pathfinder_npc was affectionately named "Hector" by the
now-defunct Swarm Armory community.
AI: set default horde class to jumping drones
MAPPING: allow choice in asw_trigger_fall

Previously, mappers were only able to kill NPCs using the trigger, and
could not filter which NPCs were killed.
CLEANUP: remove unused Release_Laptop build