Indicate when account is set as private

[Lyude]

Right now there's no way on Corebird to tell if someone's account is set as private or not. It might be a good idea to add a lock or something of the sort on the person's profile and/or their posts on the timeline.

[baedert]

I think we could just use the upper-left corner of the avatar for that, just like we use the upper-right corner for the verification status.