add CSP sources for obsolete browser prompt (#1731)

Adds script hash and explicit domain to `img-src` directive

client/configuration/webpack/obsoleteHTMLTemplate.html

@@ -1,4 +1,5 @@
 <script>
+  /** Reflect ANY changes to this script in the script hash in `server/eb/app.py` **/
   var root = document.getElementById("root");
   root.remove();
   var portals = document.getElementsByClassName("bp3-portal");