Redone my previous commit without whitespace changes in modified files.

Improved layout serialization: added documents support. Added layout
items state serialization.
Fixed code editor creation policy.
Add IModule.DefaultDocuments

Fixes problem with selection, which occurs when a module opens documents
during initialization, as well as documents being opened from saved
state.
Status bar items now appear in correct column. Fixes #16.
Update filter designer demo to support new state serialization
Merge remote-tracking branch 'remotes/upstream/master'

Conflicts:
	src/Gemini/Framework/ITool.cs
	src/Gemini/Modules/Shell/ViewModels/ShellViewModel.cs
	src/Gemini/Modules/Shell/Views/LayoutUtility.cs