[HawkNet.OWIN] AuthenticationHeaderValue.Parse exception when IncludeServerAuthorization is true

[BrightSoul]

Fixed an issue in HawkAuthenticationHandler with AuthenticationHeaderValue.Parse which would lead to an exception if IncludeServerAuthorization is set to true and client sends a value for Authorization which is empty, other scheme or missing altogether. See here this problem reproduced.

Switched to AuthenticationHeaderValue.TryParse and checked for scheme before calling AuthenticateResponse. Also added 3 unit test cases.