Fix and cleanup Translation (#61)

This patch addresses the following issue:

* Unused download script, removed to avoid confusion.
* Freezes pip versions.
* Freezes TF version.
* New download links which should have the correct data and be stable.
* Adds a verify_dataset script.

Convergence test results:
Bleu score (uncased): 25.147438049316406
Bleu score (cased): 24.649880826473236
ENDING TIMING RUN AT 2018-06-02 05:41:52 AM
RESULT,transformer,1,111840,,2018-05-31 10:37:52 PM

(Approx within 1 hour of median reported time).