Added PersistentSettings.cs:
   To save settings onto XML and load it back. Save class in xml.

Added PersistentSettingsTests.cs:
   Simple unit test for save and load.

Modify DynamoController.cs:
   Core function of save and load settings onto program.

Modify DynamoView.xaml.cs:
   Update WindowClosing to trigger controller SavePersistentSetting();