set default className if group.name doesn't defined in prop

[Sinan997]

GroupedFormPropList class was grouping under the undefined object if group.name wasn't defined in prop.

This pr sets a default className for prop if group.name is undefined.

Note

Edited by @masumulu28

We will try to manage input order (with and without group) adding group property, if it's not possible we'll accept this default behavior.