Add default for DatabaseFile

Elwig/Helpers/Config.cs

@@ -7,7 +7,7 @@ namespace Elwig.Helpers {
     public class Config {
 
         private readonly string FileName;
-        public string DatabaseFile;
+        public string DatabaseFile = App.DataPath + "database.sqlite3";
 
         public Config(string filename) {
             FileName = filename;