[RM] torchtext as a top-level package

[ruohoruotsi]

Remove torchtext as a top-level package. torchtext code was added to the repo as a workaround because:

• OpenNMT requires the latest torchtext, which must be installed with pip install git+https://github.com/pytorch/text (torchtext=0.4.0)
• The latest torchtext cannot be installed with pip install torchtext because on PyPI torchtext=0.3.1 is the latest. Using it causes OpenNMT based predictions to BREAK!

Since we cannot accelerate nor predict when torchtext=0.4.0 will be on PyPI, we fold that dependency into a top-level package and carry on with this issue as a reminder to clean up once the correct version is ready.

[ruohoruotsi]

23a6dda, 4cd125f

[ruohoruotsi]

https://pypi.org/project/torchtext/ is now at version 0.6 @Timilehin , this should be ready to go!
Also does https://pypi.org/project/OpenNMT-py/ even require torchtext anymore?