grids random payload defined

ok so next step is go on the server side
- extract recipient, amount, payload,
- register search pattern
- wait for matching transaction to appear
- notify correct party

priv/static/js/ts/grids-basic.ts

@@ -27,6 +27,11 @@ main
     let grids_url_elt = document.getElementById('grids-url') as HTMLTextAreaElement;
     let grids_png_elt = document.getElementById('grids-png') as HTMLImageElement;
 
+    let rand_data : Uint8Array = new Uint8Array(32);
+    window.crypto.getRandomValues(rand_data);
+    let hex : string = rand_data.toHex().toUpperCase();
+    p_input.value = 'text payload ' + hex;
+
     // Page initialization
     submit_btn.addEventListener(
         'click',