Update module/VuFind/src/VuFind/ILS/Driver/Aleph.php

Bugfix: Only convert month part from string to number if not already provided as number.
Error occures when input date has this format: 31/12/2013
Additional cleanup: Replaced deprecated split() with explode()
Streamlined and documented entity cleanup within stored MARC records.
Adding MultiBackend driver (VUFIND-643).