Server: add moderation tools to client

Current version have special admin console (#5388). But it can be used by server's admin only and contains broken features like table's clean/close.

It will be useful to enable **moderation support** and gives limited admin access for some users. Like ban or mute online players.

After bans architecture improves (see #6543) new features can be added to admin tools and official clients.

Admin tools improves:
* [ ] add moderators table view and edit;
* [ ] add "servers without registration" support (that's non trivial feature and must be implemented with extra password or like versa -- see current admin tools access by password);

Client/server improves:
* [ ] inform about moderator access and commands on welcome message;
* [ ] command to see user's IP (example: `/ip username`);
* [ ] command to ban/mute username (example: `/mute username_or_ip 12h used profanity and toxic`)
* [ ] revert of wrong actions must be used by admin tools only (e.g. un-ban or un-mute);