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/utils/classes/BrowserCache.js

@@ -0,0 +1,67 @@
+import { logErrorAndReturnError, logWarningAndReturnError } from '../helpers/';
+
+function supportLocalstorage() {
+  var mod = 'test-slug';
+  try {
+    localStorage.setItem(mod, mod);
+    localStorage.removeItem(mod);
+    return true;
+  } catch (e) {
+    return false;
+  }
+}
+
+export function BrowserCache(prefix, default_expire_seconds) {
+  var default_expire_seconds = parseInt(default_expire_seconds, 10) || 3600;
+
+  if (!supportLocalstorage) {
+    console.warn(['Current browser does not support localStorage.']);
+  }
+
+  return !prefix
+    ? logErrorAndReturnError(['Cache object prefix is required'])
+    : {
+      prefix: prefix,
+      seconds: default_expire_seconds,
+      set: function (key, value, expire_seconds, ret) {
+        if (supportLocalstorage) {
+          expire_seconds = expire_seconds ? expire_seconds : default_expire_seconds;
+          if (!expire_seconds) {
+            ret = logWarningAndReturnError(['Invalid cache expiration value', expire_seconds]);
+          }
+          try {
+            localStorage.setItem(
+              prefix + '[' + key + ']',
+              JSON.stringify({
+                value: value,
+                expire: new Date().getTime() + expire_seconds * 1000,
+              })
+            );
+            ret = !0;
+          } catch (error) {
+            ret = logWarningAndReturnError([error]);
+          }
+        }
+        return ret;
+      },
+      get: function (key, ret) {
+        ret = supportLocalstorage ? localStorage.getItem(prefix + '[' + key + ']') : null;
+        ret = ret ? JSON.parse(ret) : null;
+        ret = null !== ret ? (void 0 !== ret.expire && ret.expire > new Date().getTime() ? ret.value : null) : ret;
+        return ret;
+      },
+      clear: function () {
+        var k;
+        if (supportLocalstorage && Object.keys(localStorage).length) {
+          for (k in localStorage) {
+            if (localStorage.hasOwnProperty(k)) {
+              if (0 === k.indexOf(prefix)) {
+                localStorage.removeItem(k);
+              }
+            }
+          }
+        }
+        return !0;
+      },
+    };
+}