Bug 11459: use drop-down to set OrderPdfFormat syspref

This patch converts the OrderPdfFormat to a choice.

To test:

[1] Look at OrderPdfFormat in the system preferences editor. Verify
    that there is a drop-down giving a choice among the three PDF
    basketgroup printing formats.
[2] Change the OrderPdfFormat setting and print a basketgroup.  Verify
    that the chosen template is used.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>

I followed the test plan. Patch behaves as expected.
Signed-off-by: Marc Véron <veron@veron.ch>

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Improves usability of the OrderPdfFormat system preference.
Works as described, only changes YAML file.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>

koha-tmpl/intranet-tmpl/prog/en/modules/admin/preferences/acquisitions.pref

@@ -48,6 +48,10 @@ Acquisitions:
 
     Printing:
         -
-            - Use
+            - Use the
             - pref: OrderPdfFormat
-            - when printing basket groups.
+              choices:
+                  "pdfformat::layout2pages":   English 2-page
+                  "pdfformat::layout3pages":   English 3-page
+                  "pdfformat::layout3pagesfr": French 3-page
+            - layout when printing basket groups.