Add categories to the list of widgets in Insert Widget dialog

[KeyWorksRW]

Description:

While the Insert Widget does list all possible children, it often ends up being a huge alphabetized list. That's sort of okay if the user knows the name of what they want since they can start typing the name and have the list reduced to the item they want.

Presenting the possible widgets grouped into categories should make it easier to find a specific widget, which in turn would make it practical to add to the right-click context menu, as well as a tool button on the Navigation Panel.