Consolidate user editing code

Summary:
  - We currently have some bugs in account creation due to nontransactional user/email editing.
    - We save $user, then try to save $email. This may fail for various reasons, commonly because the email isn't unique.
    - This leaves us with a $user with no email.
  - Also, logging of edits is somewhat inconsistent across various edit mechanisms.
  - Move all editing to a `PhabricatorUserEditor` class.
  - Handle some broken-data cases more gracefully.

Test Plan:
  - Created and edited a user with `accountadmin`.
  - Created a user with `add_user.php`
  - Created and edited a user with People editor.
  - Created a user with OAuth.
  - Edited user information via Settings.
  - Tried to create an OAuth user with a duplicate email address, got a proper error.
  - Tried to create a user via People with a duplicate email address, got a proper error.

Reviewers: btrahan, vrana, jungejason

Reviewed By: btrahan

CC: tberman, aran

Maniphest Tasks: T1184

Differential Revision: https://secure.phabricator.com/D2569

scripts/user/add_user.php

@@ -61,14 +61,14 @@ if ($existing_email) {
 $user = new PhabricatorUser();
 $user->setUsername($username);
 $user->setRealname($realname);
-$user->save();
 
 $email_object = id(new PhabricatorUserEmail())
-  ->setUserPHID($user->getPHID())
   ->setAddress($email)
-  ->setIsVerified(1)
-  ->setIsPrimary(1)
-  ->save();
+  ->setIsVerified(1);
+
+id(new PhabricatorUserEditor())
+  ->setActor($admin)
+  ->createNewUser($user, $email_object);
 
 $user->sendWelcomeEmail($admin);