create CurrentHub.LatestHubTypes cache

- refresh with HubLifeSupport.RefreshCurrentHub
- use is in PartitionMaintenance to keep a fresher list of latest hub types
mark Hub as dead on shutdown
set CurrentHub on HubService.Start
log missing subscriber as fatal for message

- don't retry the message
- ignore if the current hub is not of the latest hub type
Merge branch 'master' of github.com:daptiv/Daptiv.Bus