Post-Train Quant LAPQ Refactoring (#473)

* Move image classification specific setup code to separate script at
  examples/classifier_compression/ptq_lapq.py
* Make ptq_coordinate_search function completely independent of
  command line arguments
* Change LAPQ command line args function to update existing
  pre-existing parser (changed CLAs perfix to 'lapq' for more clarity)
* Enable LAPQ from compress_classifier.py (trigger with --qe-lapq)
* Add pointers in documentation