Adding categories to design

In this pull-request we are adding categories to design.

@Benglin, please review.

There are couple issues with subcategories panel. Planned to create separate pull-request for fixing them.  Additionally before first resizing of leftside panel all subcategories grouped in one long-long line. It is because in MeasureOverride / ArrangeOverride is passed big length value (10000 and more).
I'm interested in removing this one, see the ```LibraryView.xaml``` comment below.