Use internal dz messages to process duration and location changes
Add world DynamicZone class (later this will inherit from a base)
Add FindDynamicZoneByID to get dz from zone and world system caches
This should eliminate race conditions caused by zones trying to set
a leader when members in different zones quit at the same time
Zone still detects when leader goes offline to trigger a change
since it's easier than having world process expedition member status
updates and perform expedition lookups
