Added using to dialog usage.
- Refactored code so that only event handlers are async void. - Refactored BoundRelayCommand and AggregateBoundRelayCommand and added static factory methods to simplify use. - Added AsyncRelayCommand to handle asynchronous operations. - Updated some comments and headers.
Refactored commands that depend on a collection of child properties to use composition instead of inheritance and added static factory methods for them.
Renamed file.
Completely refactored complex command creation to use a fluent builder syntax.