Fix unit tests for widget handler

This patch is changing the way in which manifest
and application objects are created.
All below tests now pass:
 - WidgetHandlerTest.ParseManifestWithAllOfOtherItemsAndOnePreferenceItem
 - WidgetHandlerTest.ParseManifestWithAllOfOtherItemsAndThreePreferenceItemsList
 - WidgetHandlerTest.ParseManifestWithOnlyNameAndVersion