feat(App): Loads mode extensions on demand (#3312)

* feat: Dynamic plugin imports

* Remove unused file

* Fix basic dev mode

* Fix the modes issue that Joe requested

* Merge fixes

* Add the ability to publish directory contents

* PR review changes

---------

platform/public/demo.html

@@ -0,0 +1,9 @@
+<html>
+  <body>
+    <h1>Demo Page</h1>
+    <p>This demo page shows how to include directories of content in the pluginConfig.json file.
+      The idea is that it is possible to serve up non-compiled content such as the microscopy mode
+      which will not be included in the compile of OHIF but can be included later on dynamically.
+    </p>
+  </body>
+</html>