Bug 16127 - Add discharge menu item to patron toolbar

Bug 16127 - Add discharge menu item to patron toolbar

This patch changes the "Discharge" menu in the patron sidebar to read
"Discharges," and adds a "Discharge" menu item to the patron toolbar.

This adds some redunancy, but fits with the pattern of including "views"
in the sidebar and "actions" in the menu. The discharge feature can be
thought of either way.

To test you must have the 'useDischarge' system preference enabled.

- View the detail page for any patron.
- Confirm that the sidebar menu reads "Discharges."
- Confirm that the "More" menu contains a "Discharge" link which works
  correctly.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>