UserList Improvements

-- This is my latest and last attempt with this.

Changes:
- Better GUI
- Added "Search Box"
- Added Multi-Select
- Added "Last Seen"

- If server does not support "last seen function" empty columns are hidden

Known bugs:
- Date and Time are not in UTC
- Deleting ~4000 "inactive accounts" can take a while (but this is not my fault)
- Windows title should be changed to "User List (1337 items)"

More important, my programming skills are not that good as I wanted, so if something is wrong in this patch - simply fix it, commit and move forward - if not leave it and use old ugly User List for another two years.

Preview:
![User_List_-_2948_-_Registered_Users_2013-03-02_08-53-24](https://f.cloud.github.com/assets/521035/212560/5854f254-830e-11e2-9603-bcc962ad50e9.png)
![User_List_-_2948_-_Registered_Users_2013-03-02_08-53-40](https://f.cloud.github.com/assets/521035/212561/5c71713c-830e-11e2-8e63-bbb580a10693.png)