Refactoring to reduce code duplication

* Reducing duplicate code in network operations.
* Simplifying the related exception handling chain.
* Introduce strict session for handling POST redirects by
  keeping the request method for POST and reissue the same request
  body.
* Depend on the (just released) latest version of Requests library.
* Remove zot_ prefix on functions.
* Created convenience function for AES decapsulation of JSON data,
  which also reduces code duplication and simplifies the related
  exception handling.