Add "Mailing List" users

Summary:
Ref T8387. Adds new mailing list users.

This doesn't migrate anything yet. I also need to update the "Email Addresses" panel to let administrators change the list address.

Test Plan:
  - Created and edited a mailing list user.
  - Viewed profile.
  - Viewed People list.
  - Searched for lists / nonlists.
  - Grepped for all uses of `getIsDisabled()` / `getIsSystemAgent()` and added relevant corresponding behaviors.
  - Hit the web/api/ssh session blocks.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: eadler, tycho.tatitscheff, epriestley

Maniphest Tasks: T8387

Differential Revision: https://secure.phabricator.com/D13123

scripts/ssh/ssh-exec.php

@@ -182,11 +182,11 @@ try {
       'P' => $user->getPHID(),
     ));
 
-  if (!$user->isUserActivated()) {
+  if (!$user->canEstablishSSHSessions()) {
     throw new Exception(
       pht(
-        'Your account ("%s") is not activated. Visit the web interface '.
-        'for more information.',
+        'Your account ("%s") does not have permission to establish SSH '.
+        'sessions. Visit the web interface for more information.',
         $user->getUsername()));
   }
 

scripts/user/account_admin.php

@@ -125,7 +125,7 @@ if (strlen($password)) {
 
 $is_system_agent = $user->getIsSystemAgent();
 $set_system_agent = phutil_console_confirm(
-  pht('Is this user a bot/script?'),
+  pht('Is this user a bot?'),
   $default_no = !$is_system_agent);
 
 $verify_email = null;
@@ -165,7 +165,7 @@ printf($tpl, pht('Password'), null,
 
 printf(
   $tpl,
-  pht('Bot/Script'),
+  pht('Bot'),
   $original->getIsSystemAgent() ? 'Y' : 'N',
   $set_system_agent ? 'Y' : 'N');