fix getPreference function

the getPreference would only check the URL parameter and not the actual preferences for the key "application_language".
This resulted in an always-English frontend independent of the preferences set in the prefs file

Co-Authored-By: Daniel Röwenstrunk <929533+roewenstrunk@users.noreply.github.com>

app/controller/PreferenceController.js

@@ -72,7 +72,11 @@ Ext.define('EdiromOnline.controller.PreferenceController', {
 	        var lang = me.getURLParameter("lang");
 	        if(lang) {
 		        return lang;
-	        } else {
+	        }
+            else if(me.preferences[key]) {
+                return me.preferences[key];
+            }
+            else {
 		        return "en";
 	        }
         }