7.0 pos backup draft orders

Propose 'pos_backup_draft_orders' in 7.0 serie.

This PR has been previously approved on launchpad:
* @pedrobaeza :+1:  2014-07-30

Ref: https://code.launchpad.net/~sylvain-legal/openerp-pos/7.0_pos_backup_draft_orders/+merge/228829