Support Reply-To headers in ticket filters

The email filtering feature supports a 'Use Reply-To' feature, but seems to
never have been implemented. This patch officially supports using the
Reply-To email header as the From header for emails matching the filter.
Merge pull request #669 from greezybacon/feature/filter-reply-to

Support Reply-To headers in ticket filters

Reviewed-By: Peter Rotich <peter@osticket.com>