Change the way the debugging library is build and found, yet again.

We used to build a helper library as part of the project. First with the
qmake -after SOURCES= stuff and after until now with the
gdbmacrosbuildstep. Now, the all new and fancy integretation directtly
into the qt version dialog. You build the debugger library once for
each qt version and then it's there ready to be loaded into each
project build against that qt version. Saves a lot of time.
And makes it possible to also load that library into while debuggign a
cmake project. (Need to hook that up now.)
Unfourtanetly this breaks the custom dumpers if you use a custom run
executable.