Add config and basic page template support

* load JS file asyncronously (just HTML5 async attribut)
* add basic support for page template, where it generates the code inside
  of a simple div at the top
* added option to turn off QR code support

lib/Configuration.php

@@ -52,6 +52,7 @@ class Configuration
             'languageselection'        => false,
             'languagedefault'          => '',
             'urlshortener'             => '',
+            'qrcode'                   => true,
             'icon'                     => 'identicon',
             'cspheader'                => 'default-src \'none\'; manifest-src \'self\'; connect-src *; script-src \'self\'; style-src \'self\'; font-src \'self\'; img-src \'self\' data:; referrer no-referrer; sandbox allow-same-origin allow-scripts allow-forms allow-popups',
             'zerobincompatibility'     => false,