Add splitter between columns in Inspector.

Add add ellipsis if property names are truncated. Fixes #89.
added nullable double value to the demo
Merge branch 'master' of github.com:mwpowellhtx/gemini

Conflicts:
	src/Gemini.Demo/Modules/Home/ViewModels/HelixViewModel.cs
	src/Gemini.Modules.Inspector/Inspectors/TextBoxEditorView.xaml