Add ReadXmlData() method to ActionBasics

* Adds the ReadXmlData() method to ActionBasics abstract class, and
  implements this method in all inherited classes. (Some implementations
  are currently stubbed).
* ReadElement() added to ExtensionMethods to extend the XmlReader class
* SkipToNextElement() added to ExtensionMethods to extend the XmlReader
  class
* GetElementCount() added to ExtensionMethods to extend the XmlReader class
* Add some null checks around methods in Account class
Add methods to load data from saved XML files

Add methods to obtain application and account data from the saved XML
files.