Changed parameters to accept IUnityContainer

 - Its nice to ask for a Interface instead of the concrete
implementation in method parameters. Since the package
Unity.AspNet.WebApi uses interface IUnityContainer to configure a Unity
in a WebApi, we should also use the interface IUnityContainer in
HangFire. And its compatible with clients already using this package.
Merge pull request #1 from xavero/master

Changed parameters to accept IUnityContainer