Added a remove function

This is a proposed fix for issue msurguy#35 - duplicated spinner.  When calling the new remove function, the spinner is removed from the DOM, preventing a build up of duplicate spinners.

dist/ladda.js

@@ -47,6 +47,10 @@
                 }, 1e3);
                 return this;
             },
+            remove: function() {
+                spinnerWrapper.parentNode.removeChild(spinnerWrapper);
+                return this;
+            },
             toggle: function() {
                 if (this.isLoading()) {
                     this.stop();
@@ -157,4 +161,4 @@
         create: create,
         stopAll: stopAll
     };
-});
+});