In ticket/11451 this was not correctly changed to reflect the new class
phpbb_notifcation_method_messenger_base. Additionally, an undefined
variable error has been fixed in messenger_base.php (change should be
confirmed by bantu though).
PHPBB3-11488
Make sure the user has an email address set before offering email
notifications. The address could be missing for whatever reason, e.g. external
authentication. This is also consistent with XMPP/Jabber now.
PHPBB3-11452
Create a very basic user loader class to handle querying/storing
user data in a centralized location.
Use DIC collection service for notification types/methods.
Cleanup unused dependencies.
Fix some other issues.
PHPBB3-11103
