Other:
- Filtering users and groups, and implement it in backends
- Proper cross-check between user and group SIDs.
- Issue a warning if Unix/Samba account settings are not consistent with
  each other (e.g the group of primary group ID != group of primary group SID).
- Other consistency checks (unique user/group IDs, unique SIDs, etc...).
- Copy data between backends.
- Update docs

And some TODOs from the past which are still unsolved:
- Add 'Help' button to user and group properties dialogs.
- Add right mouse popup
- Replace call of rm with own procedure.
- Use QFile for file operations.
- 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?