[FIX] Add context propagation for m2m list view (7.0 lp:1279885)

Fix bug https://bugs.launchpad.net/openerp-web/+bug/1279885 :
    Many2many fields in Tree views will not get translated.
    If you check the context for a name_get of a m2m field, it is passed as
    None.

Add context propagation to m2m fields in list views.
Fix translation issues when viewing a a many2many field in a Tree view.