Move user info, proxy credentials and application version

Move user info, proxy credentials and application version into RaygunClientBase. This lets us use one method to set those properties on standard, web api and mvc RaygunClient objects as they all implement that class. Like this:

````csharp

    public static RaygunWebApiClient GetWebApiRaygunClient()
    {
      return (RaygunWebApiClient) AddVersionToRaygunClient(AddUserToRaygunClient(new RaygunWebApiClient()));
    }

    public static RaygunClient GetRaygunClient()
    {
      return (RaygunClient) AddVersionToRaygunClient(AddUserToRaygunClient(new RaygunClient()));
    }

````