use data:;base64 instead of file in favicon

pywebio/html/js/pywebio.js

@@ -1045,8 +1045,8 @@
     function WebIOController(webio_session, output_container_elem, input_container_elem) {
         WebIOSession_ = webio_session;
         webio_session.on_session_close = function () {
-            $('#favicon32').attr('href', 'image/favicon_closed_32.png');  // todo:remove hard code
-            $('#favicon16').attr('href', 'image/favicon_closed_16.png');
+            $('#favicon32').attr('href', 'data:image/png;base64, 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');
+            $('#favicon16').attr('href', 'data:image/png;base64, iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAA0ElEQVQ4T62TPQrCQBCF30tA8BZW9mJtY+MNEtKr2HkWK0Xtw+4NbGysxVorbyEKyZMNRiSgmJ/tZufNNzO7M0ThxHHc8zxvSnIIoPNyXyXt0zRdR1F0+gxhblhr25IWJMcA3vcFviRtSc6DILg5XyZ0wQB2AAbFir7YBwAjB8kAxpg1ycmfwZlM0iYMwyldz77vH3+U/Y2rJEn6NMYsSc7KZM+1kla01p4BdKsAAFwc4A6gVRHwaARQr4Xaj1j7G2sPUiOjnEMqL9PnDJRd5ycpJXsd2f2NIAAAAABJRU5ErkJggg==');
         };
 
         this.output_ctrl = new OutputController(webio_session, output_container_elem);