Gntools

- Added internationalization (i18n) module
- Completed ELE definitions
- Fixed bugs in geometry module
- Fixed bugs in protocol logger
- Added geometry serialization tests

- Removed get_field_name() method from PlanHelper class, added several new properties instead to allow for maximum flexibility.
- Added definitions module with DefinitionTable and RelationTable classes (among others).
- Added common.const module (partially shadows gpf.common.const) with GEONIS constants.
- Improved docstrings.

- Added dependency on specific GPF version (setup.py)
- Improved GN protocol logger
- Improved GN datasource reader