Fix all target="_blank" anchors to be safer

Fixes #1411

static/js/ng-safenewtab.js

@@ -0,0 +1,10 @@
+/**
+ * Adds both target="_blank" and rel="noopener" to the marked anchor tag.
+ * Background on noopener: https://mathiasbynens.github.io/rel-noopener/
+ */
+angular.module('quay').directive('ngSafenewtab', function () {
+  return function (scope, element, attr) {
+    element.attr('target', '_blank');
+    element.attr('rel', 'noopener');
+  };
+});