Import libtextclassifier code and models.

This fixes a problem where models were not unmapped.

Also includes updated model files from some Tier-1 languages and
improved tokenization for cjt.

Switch back to dynamic linking of protobuf-lite library.

Bug: 37446398
Bug: 36886059
Test: Unit tests pass.
Change-Id: I5f9e8747918f49d8f1f7c65f3b8a6610141795df