MetaMTA - lay some ground work for having an application

Summary:
Ref T5791. This does a few bits there. Namely:

 - Adds PHID column to PhabricatorMetaMTAMail
   - Implements a PhabricatorMetaMTAMailPHIDType
   - Script to backpopulate them.
 - Makes PhabricatorMetaMTAMail implement PolicyInterface.
   - View policy is NOONE and the author and recipients have automatic view capabilities
   - No edit capability.
 - Adds a PhabricatorMetaMTAMailQuery for PhabricatorMetaMTAMail.

Test Plan: ran `./bin/storage upgrade` successfully. commented on a maniphest task and verifed the metamta mail object in the database was created successfully with a shiny new phid

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5791

Differential Revision: https://secure.phabricator.com/D13394

resources/sql/autopatches/20150622.metamta.1.phid-col.sql

@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_metamta.metamta_mail
+  ADD phid VARBINARY(64) NOT NULL AFTER id;

resources/sql/autopatches/20150622.metamta.2.phid-mig.php

@@ -0,0 +1,22 @@
+<?php
+
+$table = new PhabricatorMetaMTAMail();
+$conn_w = $table->establishConnection('w');
+
+echo pht('Assigning PHIDs to mails...')."\n";
+foreach (new LiskMigrationIterator($table) as $mail) {
+  $id = $mail->getID();
+
+  echo pht('Updating mail %d...', $id)."\n";
+  if ($mail->getPHID()) {
+    continue;
+  }
+
+  queryfx(
+    $conn_w,
+    'UPDATE %T SET phid = %s WHERE id = %d',
+    $table->getTableName(),
+    $table->generatePHID(),
+    $id);
+}
+echo pht('Done.')."\n";

resources/sql/autopatches/20150622.metamta.3.phid-key.sql

@@ -0,0 +1,2 @@
+ALTER TABLE {$NAMESPACE}_metamta.metamta_mail
+  ADD UNIQUE KEY `key_phid` (phid);