User listing using JList instead of JComboBox

[KwangYul Seo]

Hi,

I have slightly modified UserManagerPanel class to use JList/JScrollPane instead of JComboBox for user listing.
It was convenient for me to manipulate user lists using JComboBox. I attached the modifed class.
It's perfectly okay if you don't accep it :)

Thanks,
Kwang Yul Seo