Code cleanup part #1: move all the services and directive JS code in the app.js file into its own files

static/js/directives/fallback-src.js

@@ -0,0 +1,14 @@
+/**
+ * Adds a fallback-src attribute, which is used as the source for an <img> tag if the main
+ * image fails to load.
+ */
+angular.module('quay').directive('fallbackSrc', function () {
+  return {
+    restrict: 'A',
+    link: function postLink(scope, element, attributes) {
+      element.bind('error', function() {
+        angular.element(this).attr("src", attributes.fallbackSrc);
+      });
+    }
+  };
+});