7.0 export partner and address

Completion of the magentoerpconnect_export_partner module to fix the export of partners and add the export of addresses.

This PR depend of this one and need to be merged after : 

* [ ] https://github.com/OCA/connector-magento/pull/33

Initial proposal on lauchpad : 
https://code.launchpad.net/~akretion-team/openerp-connector-magento/7.0-export-partner-and-address/+merge/224180
I am not sure, I thought it was meant to do the other way : If I export an address, I first export the partner using ```self._export_dependencies()```. 
But in my case, I export a partner, and then I want to export the linked address if any. It is the opposite of dependency no?

I took a look at ```def _export_dependencies```, and even if I is right to use it in my case, after an export, I am not sure it is appropriate because the magento.address take different mandatory field than backend_id but it takes magento_partner_id.
So if I give my address record to self._export_dependency(), it won't create binding properly.

But I may miss an important point here!