Bug 20676: svc/barcode should allow barcode to be printed without text

Bug 20676: svc/barcode should allow barcode to be printed without text

Test plan:

1) Point web browser to
   <staff url>/cgi-bin/koha/svc/barcode?barcode=*12345*&notext=1

   This will display a png image of the barcode *12345* with the
   text *12345* printed below the scannable barcode.

2) Apply patch
3) Refresh the browser. The human readable text no longer appears.

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>