Username validator defaults to requiring an email even if userType is not UT.email

[richardhaven]

        widget.userValidator ?? FlutterLogin.defaultEmailValidator;

This should set specific validators based on userType (which might want an alias like userNameType)

To Reproduce
Steps to reproduce the behaviour:

1. run an app with a FlutterLogin.userType = UserType.text;
2. enter a non-email username
3. submit
   Note the error message: Invalid email!

Expected behavior
appropriate validate for each value of UserType

Screenshots

Workaround
Set an explicit validator