Added the `translate` module for MT

- Removed the un-used import in `align/gdfa.py`
- Added the translate module with `model.py` to load pre-calculated phrase table and language models and
- added `stack_decoder.py` to perform stack_decoding for Statistical Machine Translation (SMT)
@alvations, please explicitly subclass from object, since we're still supporting Python 2 and it's recommended practice still.