Allow specification of a different documentmanager for the CLI script

I have a case where I need to use different MongoDB servers for different portions of the same ZF2 application. The application itself works with the setup, but the command-line tool defaults to `doctrine.documentmanager.odm_default`, which prevents me from generating hydrators, schema, etc...

This PR checks a new, optional parameter I've added to all of the ODM-related commands called `documentmanager`, which allows the person executing the script to give a name to use instead of `odm_default`.

See https://github.com/doctrine/mongodb-odm/pull/725 for more information.

Both this PR and the one I linked above are individually backwards-compatible, so they can be merged in any order.