Removed NativeAppAct., had to refactor FullParser

* Removed NativeAppActivity
* Because I removed the NativeAppActivity I had errors in the project
  and tests, but not only in the native app tests but also in the XML
  Serializer and Parser Tests.
  NativeAppActivity was abused as a global place to get a Context from.
* Refactored FullParser to only contain static methods and gave it a
  private constructor.
* Moved a function from FullParser to new class XmlTestUtils because it
  was only used there. Class is package private (default accessibility
  modificator) because it's only used and meant to be used inside the
  XML test package.