Implement breadcrumb navigation

[henhuy]

Implement breadcrumbs like this:

You can use django-cotton ones again if you want to.
Should get a list of dicts containing title and link (as django namespaced link).
For upper example this would be:

[
    {"title": "Startseite", "url": "index"},
    {"title": "Herausforderungen und Chancen": "explorer:challenges"},
    ...
]

Last item (current view) should be active (see image).