Added optional argument to ODM console commands to allow specification of a document manager

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 creates a new, optional parameter on all ODM-related commands called `documentmanager`, which allows the person executing the script to give a name to use instead of `odm_default`.

I've sent another PR to the [doctrine/DoctrineMongoODMModule repository](https://github.com/doctrine/DoctrineMongoODMModule/pull/92) with the rest of this. They are both individually backwards-compatible, so they can be merged in any order.