Added tests for undo/redo operations on implicit and explicit lists.
Fixed bug where explicit collection was not handled correctly when resetting a XamlProperty.
Added tests for undo/redo operations on implicit and explicit dictionaries.
Added tests for clearing explicit lists and dictionaries.
Fixed so an IDictionary item is removed using the item key.
Merge pull request #470 from gumme/WpfDesignerCollectionUndoFix

Wpf designer fixes for explicit collection and dictionary