fix(angular.bootstrap): only allow angular to load once

This is hard to test as a unit-test, since it involves the actual loading
of angular, but it turns out that it is easy to test using a protractor
e2e test.

Closes #5863
Closes #5587

src/angular.suffix

@@ -1,3 +1,9 @@
+  if (window.angular.bootstrap) {
+    //AngularJS is already loaded, so we can return here...
+    console.log('WARNING: Tried to load angular more than once.');
+    return;
+  }
+
   //try to bind to jquery now so that one can write angular.element().read()
   //but we will rebind on bootstrap again.
   bindJQuery();