Yodii.Lab: fully-functional Configuration editor. (...)

- Access: ConfigurationEditor button on Ribbon.
- Can add/remove layers and configuration items, complete with error display.
- Strictly bound on observable ConfigurationManager model.
- Fake initial layers are added in MainWindow.xaml.cs. Will probably remove those on next commit.
- Added dependency to Extended WPF toolkit (NuGet).
- Replaced the WpfExtensions zoom box by the Extended WPF Toolkit one.