Transitional change to restore app/Listeners empty folder

Summary:
This is a follow-up for change e66d71b8.

Tests are currently broken on fresh installations,
as we don't have any listener.

D445 will add listeners, but until it's merged, this
change will take care of the folder creation.

Test Plan: phpunit tests/Providers/EventServiceProviderTest.php

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D457