Icon-O-Matic: improve default sidebar list heights

[humdinger]

hrev57215 introduced split views for the Path/Shape/Transformer/Properties lists at the sidebar. Nice!

It'd be nice to save the split view heights with the user settings on close. Maybe as a sort of proportion of the window size, so the user setting is kept with small and fullscreen windows?

The default sizes could be better: The Transformer list could be the smallest, as there are only 3 Transformers around. The Properties should just large enough to hold the 5 lines of the the Contour/Stroke transformers. The Shapes list might be the tallest, because it normally holds the most items.