Fixes: Progress to the cmake plugin

Details:  Add a dialog asking for command line options and build
directory. This dialog pops up if you don't have a .user file. Note,
though that it also pops up if there is already a in source build.
(The build directory lineedit should be read only then.)
The cmake button in that dialog and the output pane need more polish to
make them better. With those changes you can now build and run marble
from Qt Creator. (For marble you need to pass a few options to cmake.)

Also add a configuration page to the Tools/Options dialog, where you can
specify the cmake executable path.

And add a class which runs cmake in the background to find out which
version and wheter that cmake version has Qt Creator generator. (Which I
did begin to write.)