Bug 7310: DB revision for Improving list permissions

Bug 7310: DB revision for Improving list permissions

DB revision for improving list permissions.
Adds new table virtualshelfshares for maintaining shared private lists.
Adds three columns to virtualshelves for permissions per list.
Adds column borrowernumber to virtualshelfcontents.

Feb 16, 2012: Rebased.

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Feb 28, 2012: Added three FK constraints for QA (for owner/borrowernumber in virtualshelves, shelfcontents and shelfshares). Tested update again.
Also removed the note about public lists, made obsolete by earlier adjustments for comments from Owen.
Feb 29, 2012: Rebased. Added an update statement to replace invalid borrowernumbers with null in virtualshelves before adding constraint and added a delete statement for private lists without owner now (as a result of the first step). Tested it again.
March 5, 2012: Rebased.
March 19: Rebased.
March 21: Rebased.