LP#1210161: Finish renaming bookbag to list

LP#1210161: Finish renaming bookbag to list

The JSPAC bookbag feature was renamed to "Lists" in TPAC, but several
references still exist to "bookbag", "book bag", "Book Bag", etc. in the
public and staff interfaces. This commit attempts to provide simple and
clear replacements for the old term. In some cases "list" seems best,
but where the context is uncertain "book list" is used to err on the
side of clarity. Some of these changes may be in old code that is no
longer used.

This commit also includes two minor wording changes - one to fix grammar,
and the second to update instructions for sharing a list.

Signed-off-by: Remington Steed <rjs7@calvin.edu>