Honor dcerpc_mapiproxy:samdb_url parameter when available

And use machine account credentials when loading Samba environment in OCS manager

This make it work when OpenChange is running in a domain member instead of in the DC host.
Fix autodiscover URLs when the OpenChange is behind a proxy

Check first HTTP_X_FORWARDED_HOST header instead of HTTP_X_FORWARDED_SERVER
as OpenChange may be proxied and the client is unable to this server directly.
Added copyright note
Merge pull request #67 from Zentyal/ejhernandez/ocs-manager-separated-deployments

Autodiscovery returns something useful when OC is not in DC