URL Navigator improvements:
* Get rid again of the "Go Up" button.
* Add the possibility to show the full path of an URL also in the breadcrumb mode.
The setting can be changed by the context menu of the URL Navigator.

* Improve the drop-down button and show all paths until the root.
This allows to go up the hierarchy in an easy manner also if the "show full path" setting is disabled.

* Represent the host as a button when sub paths are shown.
Users had problems to go back to the root node as they did not assume that clicking on the host-editor brings them back. So now the host editor is only shown if no sub paths are present.