It seems some people cannot live without a tree view ;-)

So Dolphin will provide a dock which contains the directory hierarchy, which will be synchronized with the active view. It does not clutter the UI (the dock can be turned off), but makes happy a lot of users -> kind of win-win-situation.

This commit provides only a rough initial version, which shows the current URL as tree. I'll work on the interaction during the next week(s)...