Npc event anomaly spawn

[MikeJeffers]

Features a new rift that:

• Spawns on an event (now: NPC boss death; future: anything that can send SpawnPortal message)
• Be targeted to any zone and any location
• Be targeted to multiple locations w/ weights (for random selection)
• Have limited lifespan (despawn timer)
• Have limited uses per lifespan (max number of jumps)
• Have robot class restrictions of arbitrary types (list of category flags)

See the OPDB PR for the datamodel schema changes.
REQUIRES: OpenPerpetuum/OPDB#254

Closes: #245