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