Add second timestamp copy button.

When two timezones are displayed there is now a button to copy each of
the timestamps.

clock.js

@@ -47,8 +47,8 @@ function startTime(){
   //document.getElementById('JStz').innerHTML = current_tz;
 }
 
-function copy_timestamp() {
-  var copyText = document.getElementById("time_body").innerText;
+function copy_timestamp(to_copy) {
+  var copyText = document.getElementById(to_copy).innerText;
   var temp_element = document.createElement("textarea");
   document.body.appendChild(temp_element)
   temp_element.value = copyText;