FEATURE: Load jQuery if not present

Dynamically loads jQuery if it is not already present when the script
loads. This makes using the plugin easier on pages that do not already
load jQuery in their head.

Resources/Public/js/cachevisualisation.js

@@ -1,5 +1,4 @@
-$(document).ready(function () {
-
+function initialize() {
   $('div[data-vivomedia-cache-visualisation]').hover(
     function() {
       var container = $( this );
@@ -33,4 +32,15 @@ $(document).ready(function () {
       }
     });
   });
-})
+}
+
+if (window.$) {
+  $(document).ready(initialize);
+} else {
+  var script = document.createElement('script');
+  script.src = 'https://code.jquery.com/jquery-3.4.1.min.js';
+  script.setAttribute('integrity', 'sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo=');
+  script.setAttribute('crossorigin', 'anonymous');
+  script.addEventListener('load', initialize);
+  document.head.appendChild(script);
+}