Consuming composite URL set in Heroku case

- use the Application.load method in the event of a composite URL

- don't pass application URL to Client constructor (that functionality has been moved to Application.load in the composite URL-case, and client.applications.get in the non composite-URL case)
Merge pull request #18 from stormpath/features/conditionally_use_heroku_composite_url-7

Consuming composite URL set in Heroku case