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The LICENSE file says everything is 3-clause BSD, which is what we want,
but at some point the Apache license was added to the top of some files
and that proliferated. This commit removes the Apache license from any
files that we own the copyright to.

Also updates the copyright year and removes the unnessary coding=utf-8
line.

Also includes following changes for inter-layer model-parallel implementation:
- Refactoring of model implementations
- Training loop changes to support inter-layer communication using `ring_exchange`
- New groups for inter-layer communication
- Checkpoint changes
- Command line arguments