Multitenancy

### Support multi company
* New command `openchange_neworganization --firstorg=NAME_OF_THE_ORGANIZATION`
* Add users using `openchange_newuser --create --firstorg=NAME_OF_THE_ORGANIZATION whatever@foo.com`
* User log in with their full email address
* Users only see contacts from their organization

### Requirements before merging to building branches
* It will require to do migration of data.
 * `openchange_provision --migrate` (it's idempotent)
* It will require changes in zentyal code
 * Add `--firstorg` attribute to every openchange_* command
No sanity check performed on username or cn. What if cn points to NULL?