NN-1947 Add configuration so software using this library can alter the URL Query Parameter
- Support setting the authorization header names just in case someone needs to change 'em.
- Move RequestConstants into RequestConfiguration now that no other code uses the Constants.
- Add RequestConfiguration Builder so ReqConf is immutable.
- Update hurl CLI to include header configurability
Merge pull request #37 from bazaarvoice/jrogers-add-config

Jrogers add RequestConfiguration to permit customizing headers and query parameter.