retry sql when connection from pool was stale
add Hub.IsDead flag to database
update QueuePartitionLocker to handle partitions locked by dead hubs
add CurrentHub as singleton

Conflicts:
	Druq.Hub/Messaging/IdempotencyService.cs
HubLifeSupport updates local cache of dead and active hubs
PartitionMaintenance clears dead hub message locks
add tests and fix bus for removing dead hub locks from messages
add logging
Merge pull request #57 from daptiv/fix-hub-life-support-perf

- [ ] @EEE3 please test