Lp 1843079: Add renewals remaining to AutoRenew reactor's user data

Lp 1843079: Add renewals remaining to AutoRenew reactor's user data

Add a renewal_remaining field to the autorenew event's user data so
that we can report the number of renewals remaining to the patron
without doing (possibly erroneous) math in the template.  When the
circulation is renewed, we use the renewal remaining count from the
new circulation.  When the renewal fails, we use the number from the
original circulation.

The current template is not modified to add this field.  That is left
as an exercise for sites that want to add this information for the
convenience of their patrons.

Signed-off-by: Jason Stephenson <jason@sigio.com>