Pathauto token [crumbs-parent] based on crumbs breadcrumb.

We need to be careful with this.
- If both the pathauto plugin and this token thing are enabled, we get a circular dependency.
- Crumbs can change a lot (each time you set a new taxonomy term for a node, change the menu, etc). But we want aliases to remain stable.
- Aliases might become too long if we use crumbs to produce them.

So, altogether, it seems like a very problematic idea.

Postponed for now.