Added support for storage retrieval requests in VuFind core code
- added support in Voyager/VoyagerRestful drivers (call slips in Voyager land).
- Extended Demo ILS driver to handle holds and storage retrieval requests properly.
- Minor fixes to comments, etc.
Fixed the "You must be logged in first" response from AJAX checkRequestIsValid call.
Updated language file (courtesy of Hugo Agud).
Turn off Voyager callslips by default.
Merge commit 'ef08ee22d5126ae4c3e4ab9815c9fa1e30aa3c35'