Add Visible modes function from Organisation to Users too (#16069)

You can limit or hide organisations. This pull make it also posible for users

- new strings to translte
- add checkbox to user profile form
- add checkbox to admin user.edit form
- filter explore page user search
- filter api admin and public user searches
- allow admins view "hidden" users
- add app option DEFAULT_USER_VISIBILITY
- rewrite many files to use Visibility field
- check for teams intersection
- fix context output
- right fake 404 if not visible

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Andrew Thornton <art27@cantab.net>

options/locale/locale_en-US.ini

@@ -724,6 +724,14 @@ email_notifications.onmention = Only Email on Mention
 email_notifications.disable = Disable Email Notifications
 email_notifications.submit = Set Email Preference
 
+visibility = User visibility
+visibility.public = Public
+visibility.public_tooltip = Visible to all users
+visibility.limited = Limited
+visibility.limited_tooltip = Visible to logged in users only
+visibility.private = Private
+visibility.private_tooltip = Visible only to organization members
+
 [repo]
 new_repo_helper = A repository contains all project files, including revision history.  Already have it elsewhere? <a href="%s">Migrate repository.</a>
 owner = Owner