TPAC bookbag CGI param changed to bbid

TPAC bookbag CGI param changed to bbid

To avoid propagating a generic URL parameter like 'id', which can be
picked up by other pages and cause breakage, use 'bbid' instead.  Also,
clear the 'bbid' param from the my-account tabs.

While we're in there, silence an uninitialized string warning.

Signed-off-by: Bill Erickson <berick@esilibrary.com>