Implements basic parts for the handling of the 'bundle' products

It does not implement the import of bundle products, but only add a hook ConnectorUnit to implement it. It adds the import of the dependencies of the bundles though.

The PHP part of the connector has been updated in order to add the
bundle information, so it needs to be updated on the Magento instance.

Original MP on Launchpad:
https://code.launchpad.net/~camptocamp/openerp-connector-magento/7.0-next-release-bundle-import-base/+merge/223716