Remove callback async code
Merge pull request #122 from AnthonySteele/no_async_callbacks

Remove callback async code
Created class to handle OAuth Header generation using crenna oauth for GET requests only
Now signs get request using Authorization header, but not with user tokens
Fully implemented GET oauth via headers, cleaned up tests and added OAuthHeaderData to encapsulate params for creating OauthHeaders
Merge branch 'oauth-headers' of github.com:gregsochanik/SevenDigital.Api.Wrapper into oauth-headers