DolphinQt: and so it begins

This adds the beginning of the DolphinQt user interface. It doesn't do anything useful yet and only builds via CMake.
In the new and beautiful Qt-world, can we make some kind of dolphin-law that bans such #ifdefs? If really needed, you could encapsulate such functionality into functions. The compiler can easily optimize it out, and it doesn't make the code ugly and confusing.