[IZPACK-1148] - Validate TargetPanel input and ShortcutPanel input on Windows

This is to address: http://jira.codehaus.org/browse/IZPACK-1148

Upon hitting next, apply the following constraints provided by http://msdn.microsoft.com/en-us/library/aa365247.aspx (see the reserved characters under Naming Convention). Also the link does not explicitly say it but directories cannot start or end with a space.