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>

models/fixtures/user.yml

@@ -508,7 +508,6 @@
   num_repos: 0
   is_active: true
 
-
 -
   id: 30
   lower_name: user30
@@ -525,3 +524,20 @@
   avatar_email: user30@example.com
   num_repos: 2
   is_active: true
+
+-
+  id: 31
+  lower_name: user31
+  name: user31
+  full_name: "user31"
+  email: user31@example.com
+  passwd_hash_algo: argon2
+  passwd: a3d5fcd92bae586c2e3dbe72daea7a0d27833a8d0227aa1704f4bbd775c1f3b03535b76dd93b0d4d8d22a519dca47df1547b # password
+  type: 0 # individual
+  salt: ZogKvWdyEx
+  is_admin: false
+  visibility: 2
+  avatar: avatar31
+  avatar_email: user31@example.com
+  num_repos: 0
+  is_active: true