Added test cases to db_additions_test and fixed exposed issues
Fixed copy_sptr unit tests

* Fixed rule-of-three functions for team_pokemon subclasses
* Exposed get_form_id issue, changed unit test to use get_pokemon_id
Added nature class

* Very thin wrapper around a pkmn::dict, makes it read-only
* Keys are stat names, values are stat modifiers
New nature class used by team_pokemon, not properly SWIG'd yet
nature: added [] operator for unsigned ints, added proper SWIG interfaces
swig: added CamelCase entries for nature