Introduce new /privacy group of commands

[jubalh]

Idea started here: #1827 (comment)

I think we could use something like a new /privacy command.

Recently we received

• Feature: Allow setting client identification name/version manually #1815 which let's users set their client identification (XEP-0092) name in /account.
• New Feature: Session Alarm #1827 which let's users enable a notice when more devices sign in (/session_alarm)

I think we should group them together in something like /privacy.

And maybe also include other already existing commands in there:

• /os
• /silence ?
• ..?

I also think the accounts structure can get too bloated. And we should put some things in a different structure. The settings still can be individual per account. But leave the account structure for really account related settings (I hope you get what I mean).

And things like session alarm need to be off by default and configurable by the user.
So we also need to check that preference like mentioned in: #1827 (comment)

[jubalh]

I think /privacy can also mention/forward to other commands to look at.
For example we could implement XEP-0441: Message Archive Management Preferences and add it to /mam and mention it in privacy. Similar like we do in /color where it prints:

Consistent color generation for nicks (/color)                     : OFF 
Consistent color generation in roster (/roster color)              : OFF 
Consistent color generation for occupants (/occupants color)       : OFF

[H3rnand3zzz]

Introduced in #1857, but since the design is yet to be completed, I did not introduce full set and limited it to logging, to keep things simple, especially since it's a new feature. I would suggest to add additional commands after logging integration. We can gradually introduce them or use full command reference to add all suitable commands at once.