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).
Since this is our own ```LibraryView.xaml``` (that's not available on the main Dynamo), you can do ```CTRL+K+D``` to completely format this file to fix alignment issues before committing to the pull request. It won't affect comparison with the main Dynamo.