Extended view inheritance

Task 8149: Add a `mode` (change name?) field to views, can be either `primary` or `extension`.

If `mode=primary` and `inherit_id` is set, the inherited view is fully resolved (all inheritance applied) in its own module before resolving the current view's inheritance.

This is a change from the historical cross-model inheritance, which would take the root view (model b) and apply *only* the inherited views for the current model (a), and would ignore any inheritance dealing with the root view's model.

Previous bit of review at https://code.launchpad.net/~openerp-dev/openobject-server/trunk-extended-view-inheritance-xmo/+merge/218256