* Dock panels shouldn't have any frame border or anything like that.
* They should have an external margin of 3 pixels at their border,
but then no further margins on the layouts (like sub-controls for
the pipeline state views.
* Toolbars should be Raised & Panel frames. Later we'll replace them
with actual QToolBars to better customise the painting.
* This was only added because the default tree widget controls don't
render any grid lines. Now that we're custom drawing them, the row
colors are distracting and can be confusing on themes where the
selected row is very faint.
* 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.
baldurk