[Application] Rename Application class to ApplicationData

Rename Application class to ApplicationData as a first implementation step of https://docs.google.com/a/intel.com/document/d/1N0VVlut7JCWFbAEwTQc0loN9_D2JlOXRJprQeCbXY2U/edit#heading=h.23lva9lja986

That will allow us to introduce a real Application class.