Store monitors by the host they came from and tidy up after receiving a batch
Store monitors by the host they came from and tidy up after receiving a batch

This allows us to prune monitors which don't exist on the remote host
any more if they've been deleted or renamed.

Fixes #514

jamesoff/simplemonitor,jamesoff/simplemonitor,jamesoff/simplemonitor,jamesoff/simplemonitor,jamesoff/simplemonitor