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Also merged in some changed from apex

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.

Some tests expect a clean model parallel slate and complain if a previous test left something behind; this change clears more variables that the tests complain about.

- Accumulate encoder hidden state gradient to handle skip connection
- Correctly compute the number of layers in encoder / decoder for T5 model
- Ensure e weights are initialized the same way in embeddings
- Synchronize embedding gradients across encoder and decoder for T5 model
- Support for checkpoint loading and saving

- Split a model's computation into multiple virtual stages as needed,
and schedule communication correctly between these virtual stages
- Move schedule code into `schedules.py` and communication code into
`p2p_communication.py`
- Use hyphens instead of spaces in all time logging for consistency
- Factor out code in megatron/training.py into helper functions
- Refactor evaluate() function: make it use forward_backward_schedule
functions

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

Signed-off-by: Boris Fomitchev <bfomitchev@nvidia.com>

Signed-off-by: Boris Fomitchev <bfomitchev@nvidia.com>