#455434: Bugfix for "Deserialization of entities with GSON does not work in all JVMs"

* added default constructors in package scope
* make final field non-final where necessary

Signed-off-by: Jochen Hiller <j.hiller@telekom.de>
I would not mention GSON here. The implementation of the the deserialization within the StorageService is solution specific. The change allows in general to instantiate an object by reflection and will also help for other mappers.