Parameterize playground server

_web_server/index.html

@@ -72,11 +72,9 @@ endmodule
           enableBasicAutocompletion : true,
           enableLiveAutocompletion : true
       });
-
       const log_area = document.getElementById('log');
-
       function send_to_icarus() {
-          fetch('http://localhost:8080/icarus',
+          fetch('%POSTURI%',
                 {
                     method: 'POST',
                     headers: {