Revisit template management page

Arrange templates in a group by their respective use in the system:

  * System Management Templates
  * Staff Ticket Templates (Alerts and Notices)
  * End-User Ticket Templates (Autoresponder)

This provides an interface to sort the templates and make them easier to
find and provides a nice place for new templates to be added without making
it increasingly more difficult to locate templates in the list.

This patch also fixes the missing templates in the drop-down list when
editing an implemented template.