GUI: replace .ui files

We still have these .ui files:

./GUI/View/MaterialEditor/MaterialEditorDialog.ui
./GUI/View/Toplevel/ProjectsView.ui
./GUI/View/Toplevel/SimulationView.ui
./GUI/View/Instrument/InstrumentLibraryEditor.ui

They define geometry, label, tooltip etc for GUI widgets. For many other widgets these properties are set through C++ statements.

We should unify our GUI programming style. The preferred style is direct C++ coding. We should get rid of all the .ui files. Advantages:

• Uniform style facilitates browsing of the code.
• Direct C++ coding allows us to use core functions like className().
• Direct C++ coding allows us to unify the graphical layout by using constants, inheritance, or other programming constructs.