indicate mining process

contrib/js/cuckoo_miner.js

@@ -1,8 +1,14 @@
 onready(function(){
 	document.getElementById("start_miner").onclick = function() {
+		var btn = document.getElementById("start_miner");
+		var label = btn.value;
+		btn.value = "..."
+		btn.disabled = true;
 		var worker = new Worker("./static/mineworker.js");
 		worker.onmessage = function(e) {
 		  miner_cb(e.data);
+		  btn.value=label;
+		  btn.disabled = false;
 		  worker.terminate();
 		}
 		worker.postMessage(55.0); // Start the worker.