- Use exceptions for error reporting in first_free.
  (Maybe use them later everywhere).
- Replace listbox with something standard.
- Replace all UID with type uid_t. The same with GID.
- Replace call of rm with own procedure.
- Use QFile for file operations.
- Add right mouse popup
- Add 'Help' button to user and group properties dialogs.
- Home dir permission configuration in Preferences dialog.
- Mailbox permission configuration in Preferences dialog.
- Mailbox group in Preferences dialog.
- Allow to edit GID in group properties.
- Allow to edit Group name in group properties.
- First available UID and GID in preferences dialog.
- Group quotas.
- Update last change field when changed
- After performing File/Save, and Quiting right after that requires confirming
  Save twice.  After File/Save, if one is Quiting it should be without any
  message.
- How about having group name(s) next to the Full name of a user in the upper
  panel, and similarly user names for a group in the lower pannel -- in a
  separate column?
