Sync with Google3.

 - Removes training-only fields from the model's proto.
 - Adds better English model.
 - Adds versioning and numbers.
 - Fixes utf8 string handling in JNI.

Test: Built, tested on device. Google3 tests pass.

Bug: 36885478
Bug: 34780396
Bug: 36886059
Bug: 37261597
Bug: 36886053

Change-Id: Id7801653bb9cb98e40c464b0e8eceec14b3a5dec