display a spinner when signing with a PIN

js/controllers/home.js

@@ -72,6 +72,7 @@ angular.module('copayApp.controllers').controller('HomeController', function($sc
     var credentials = pinService.get(pin, function(err, credentials) {
       if (err || !credentials) {
         $rootScope.starting = false;
+        $scope.loading = null;
         $scope.error = 'Wrong PIN';
         return;
       }

js/services/pinService.js

@@ -57,7 +57,9 @@ angular.module('copayApp.services')
           set: function(newValue) {
             this['_' + name] = newValue;
             scope.error = null;
+            scope.loading = null;
             if (newValue && newValue.length == 4) {
+              scope.loading = true;
               $timeout(function() {
                 return cb(newValue);
               }, 30);

views/home.html

@@ -103,7 +103,9 @@
             </a>
           </div>
           <div class="large-6 medium-6 small-6 columns text-right">
-            <button translate type="submit" class="button primary radius expand m0" ng-disabled="pinForm.$invalid || error">
+            <button translate type="submit" class="button primary radius expand m0" 
+              ng-disabled="pinForm.$invalid || error || loading">
+              <i class="fi-bitcoin-circle icon-rotate spinner" ng-show="loading"></i> 
               Sign in
             </button>
           </div>