Add config migration feature

Bungee/src/main/java/net/frankheijden/serverutils/bungee/entities/BungeeYamlConfig.java

@@ -75,6 +75,11 @@ public class BungeeYamlConfig implements ServerUtilsConfig {
         return config.getBoolean(path);
     }
 
+    @Override
+    public int getInt(String path) {
+        return config.getInt(path, -1);
+    }
+
     @Override
     public Collection<? extends String> getKeys() {
         return config.getKeys();