Lab: ConfigurationManager bugfixes.

- Small DRY in MainWindow.xaml.cs.
- IYodiiEngineResult.Describe() extension can now be read by humans (hopefully).

Fixed:
- Creating/destroying multiple ConfigurationManager editor window and changing ConfigurationManager content causes reentrancy.
  * Caused by multiple ViewModels still lingering (and bound) to SelectionChanged. Fixed by disposing those on close.
- Changing configuration while engine is running causes NREs.
  * Caused by unset Configuration errors in result. Fixed by using Describe() instead.