Feature-55: Enhance Python Client

[doulikecookiedough]

Summary of Changes:

• Update README.md with instructions on how to use the HashStore python client
• Refactored client module into classes HashStoreParser, HashStoreClient and MetacatDB and added new entry point method main()
• Add new pytest module test_hashstore_client
• Add functionality to interact directly with a HashStore through the python client
  • Store, retrieve and delete objects & metadata
  • Note: retrieving an object/metadata document will print a preview of the content
• Add code specifically to work with test data in knbvm (test.arcticdata.io) by querying metacat db to obtain a list of objects or metadata
  • Note: developer must manually create a pgdb.yaml file in the HashStore directory
• Add and improve documentation
• Remove redundant is_duplicate parameter from ObjectMetadata class