Migrator is now able to create real tables.

Because of how WordPress and the dbDelta function works, it's
basically impossile to test it with Unit testing.
We'll have to make sure we properly test this in acceptance testing.

lib/config/initializer.php

@@ -233,6 +233,8 @@ class Initializer {
   }
 
   public function install() {
+    $migrator = new \MailPoet\Config\Migrator;
+    $migrator->up();
     $this->log_version_number();
   }