Add a very basic logger for arethusa

This duplicates the console.log behaviour. We will still use this for
debugging purposes, but for logs we want others to see too we will use
the arethusaLogger. Jshint won't complain then - and we can still let
it track any forgotten console log statements.

app/index.html

@@ -11,6 +11,7 @@
   <script src="../vendor/mm-foundation/mm-foundation-tpls-0.1.0.min.js"></script>
 
   <script src="./js/arethusa_util.js"></script>
+  <script src="./js/arethusa_logger.js"></script>
 
   <script src="./js/arethusa.core.js"></script>
   <script src="./js/arethusa.core/main_ctrl.controller.js"></script>

app/js/arethusa_logger.js

@@ -0,0 +1,9 @@
+"use strict";
+
+/* global console */
+/* exported arethusaLogger */
+var arethusaLogger = {
+  log: function(msg) {
+    console.log(msg);
+  },
+};