Frontent dev env (#247)

* Added frontend development files/environment

* More items-categories related removals

* Improvements in pages templates (inc. static pages)

* Improvements in video player

* Added empty home page message + cta

* Updates in media, playlist and management pages

* Improvements in material icons font loading

* Replaced media & playlists links in frontend dev-env

* frontend package version update

* chnaged frontend dev url port

* static files update

* Changed default position of theme switcher

* enabled frontend docker container

frontend/src/static/js/components/media-viewer/PdfViewer.js

@@ -0,0 +1,15 @@
+import React from 'react';
+
+export default function PdfViewer() {
+  return (
+    <div className="player-container viewer-pdf-container">
+      <div className="player-container-inner">
+        <span>
+          <span>
+            <i className="material-icons">insert_drive_file</i>
+          </span>
+        </span>
+      </div>
+    </div>
+  );
+}