Merging the 'amc' branch with 'master'.
This updates the automated compression code in 'master', and adds a greedy filter-pruning algorithm.

Summary of changes:
(1) Post-train quantization based on pre-collected statistics
(2) Quantized concat, element-wise addition / multiplication and embeddings
(3) Move post-train quantization command line args out of sample code
(4) Configure post-train quantization from YAML for more fine-grained control

(See PR #136 for more detailed changes descriptions)

* For CIFAR-10 / ImageNet only
* Refactor data_loaders.py, reduce code duplication
* Implemented custom sampler
* Integrated in image classification sample
* Since we now shuffle the test set, had to update expected results
  in 2 full_flow_tests that do evaluation

* Support for multi-phase activations logging

Enable logging activation both durning training and validation at
the same session.

* Refactoring: Move parser to its own file

* Parser is moved from compress_classifier into its own file.
* Torch version check is moved to precede main() call.
* Move main definition to the top of the file.
* Modify parser choices to case-insensitive