cuttlefish: Improve Preview, Comparison views; and some C++ stuff
Wrap Preview pane in a ScrollView
No more clipping and inaccessible buttons.
Use new list types for QML properties
Fix and rework Comparison overlay sheet
Rewrite string list initialization
Clean up IconModel, prevent creation of an empty category
A fallback of categoryFromPath() is to return an empty string, which was then unconditionally passed to add() method, and that created an unnamed last menu item in Categories combo box popup.