Optimize db update notifications
Optimize db update notifications

This reduces the number of handlers that need to be registered on each
node by the number of shards it hosts. Instead of a handler for each
shard we just register one and use lists:member/2 to check if we care
about each update message.

BugzId: 13600

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb