Increase memory_limit in notifs.send.

Increase memory_limit in notifs.send.

Also do a bit of rewrite in order to limit instantiation of
$user->profile() for informations that are present in the user object.

Use PlMailer::sendTo() that set automatically the Recipient and the format
of the mail (update core to use version that uses PlMailer::setTo).

Signed-off-by: Florent Bruneau <florent.bruneau@polytechnique.org>