Update footer (issue #149)

schoolapps/templates/partials/footer.html

 <footer class="page-footer primary-color">
     <div class="footer-copyright">
         <div class="container">
-            © 2018–2019 Computer-AG, Katharineum zu Lübeck
+            <span class="left">
+                SchoolApps · Version 1.0-beta "Aebli" <br>
+            © 2018–{% now "Y" %} Computer-AG, Katharineum zu Lübeck ·
+            Licensed under <a href="http://www.gnu.org/licenses/gpl-3.0-standalone.html">GNU GPL 3.0</a>
+                </span>
             <span class="right">
+
                 <a class="grey-text text-lighten-4" href="https://katharineum-zu-luebeck.de/impressum/">Impressum</a>
                 ·
                 <a class="grey-text text-lighten-4" href="https://katharineum-zu-luebeck.de/datenschutzerklaerung/">Datenschutzerklärung</a>