Add new model fields for tracking whence a menuitem maybe came from, but defer the new attributes.
Django 1.7+ migrations are supplied, older ones, not yet.
Note that none of the functionality *supplies* the new field data yet.

The rationale is so that a call to a MenuItem, and discovering it's ancestors/children/etc should allow for yielding the original objects, where there are any.
Obviously list views etc will not necessarily map to model objects/content-types, so both fields are nullable.