Windows Phone and improved "retained" support

Hey,
I added a small project with support for Windows Phone 7 (should work on 8, too) which is tested and works fine. The main changes are the addition of the WinPhone.SocketEx library to support advanced networking and a changed version of the file logger that uses an IsolatedStorageFile.
I also added support for clearing retained messages. (Hint: they're broken on MqttDashboard.com but work fine on Mosquito).
Would be nice if you could incorporate this.
Best Regards,
Martin