issue: Canned Response Variables

This addresses issue 4756 where the `%{recipient.ticket_link}` variable is
not being replaced when the canned response is loaded in the reply box; all
other link variables work. This is due to the recipient object not being
passed to the variableReplacer which means the ticket_link is not available.
This adds the recipient object to the variableReplacer so the ticket_link
variable is properly replaced like the others on load.