Add setting to handle tiling in ProgressBars

[raeleus]

Per user Klyser8, using TenPatch for a ProgressBar knob is a minefield. Without using tiling you get odd appearances at low values:

The current solution is to just tile the whole bar, but that means you can't stretch the widget horizontally.

I propose that I develop a tileNonStretchAreas option to handle these cases. So instead of squishing non-stretching areas when they are too small, you tile them. I imagine this will solve the issue, but I'll have to do a lot of testing.