Fixes saving Sides.

-- Sides can be saved but forces cannot be copied yet.

-Minor things:
-- Deletes CLASS_MAP constant map, instead ElementModel interface has a method to get the POJO class.
-- Adds service and nation patches for JAXB classes.
-- FileIO::installDatasetFile returns true if the dataset was installed correctly, false otherwise
Adds `compareTo()` method for models. Equals operates only with IDs.