Move navigation related view code to separate module, add deprecations and tests.
Add navigation_root property to TemplateAPI (with respective test).
Make nav.pt use the new api.navigation_root property.  Document changes in CHANGES.txt.
Delete deprecated and already uncommented code.
Add an example to the docstring of INavigationRoot.  [ci skip]
Merge pull request #225 from disko/feature/INavigationRoot

Feature/INavigationRoot
Make local_navigation also respect INavigationRoot.
Merge pull request #226 from disko/feature/INavigationRoot

Make local_navigation also respect INavigationRoot.
Update message catalogs and German translation.
Make breadcrumbs respect INavigationRoot.