* NPCs now keep track of their chunk information like PlayerView does
for players
* NPCManager::sendToViewable() parallels PlayerManager::sendToViewable()
* Nano damage and debuffs now count as attacking a mob
* Mobs will de-aggro if something else killed their target
Unfortunetly, this necessitated keeping around yet more JSON objects for
the duration of the server's runtime.
It also involved unifying the way NPC IDs are handled, such that they
may be allocated and deallocated out of order.
If any NPCID-related bugs occour, this commit should be regarded as
the prime suspect.
