[IMP] Do not create FK when destination model is _auto=False

It is not useful to try to create foreign keys when the destination model is
a PostgreSQL view for example.
We already do this kind of verifications but ir.actions and transient models
but did not for _auto.
[FIX] account: prevent crash onchange company_id

(rebase of #1534)
[IMP] models: turn _patch_method() and _revert_method() into class methods

This makes the patching mechanism more flexible, and enables patching BaseModel,
for instance. This should fix #1501.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64