* Since we're promoting everything, we reset the behaviour of
RDTreeWidget so that it's not doing anything different by default.
* RDTreeWidget's interface is a bit different, exposing some useful
things like a single selected item and so on.
* We also can't set columns in the Qt Creator UI anymore, so we set them
from code.
* It seems due to deficiencies in Qt's design, there will be a
substantial need for these small custom subclasses just to add basic
functionality that should have been present in the original. So we'll
adopt a naming scheme of QFooBar -> RDFooBar for this 'almost the
same widget' type subclassing, compared to more custom/changed ones.
* GUIInvoke helper changed to use QMetaObject::invokeMethod which works
on threads better.
* LambdaThread helper class now has a thread member, it doesn't derive
from thread (this seems to be recommended practice).
baldurk