Add support for icons in discovery service.
Add support for icons in discovery service.

vivekrajenderan/simplesamlphp,tectronics/simplesamlphp,tectronics/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp,vivekrajenderan/simplesamlphp,tectronics/simplesamlphp,tectronics/simplesamlphp,tectronics/simplesamlphp