Added a way to unregister an additional openchange server (WIP)
Implemented openchangedb deprovision
Improved the usage check logic and included mailboxes usage
Improve error handling
Merge branch 'master' into cperello/deprovision-fixes
Fixed user mailbox usage check
Send error messages to stderr
Added missing import and check for mailbox status to tag it as being used
Merge pull request #12 from Zentyal/cperello/deprovision-fixes

Cperello/deprovision fixes