Bug 11505: fix untranslatable table headers in Label batch manager

The label batch manager script hard-codes the table header cell labels
in order to pass them to an HTML-building function. This obviously isn't
the best solution for internationalization, but picking the whole scheme
apart would be very complicated.

Instead this patch uses a SWITCH statement to check for each possible
case and outputs the correct translatable string for each.

To test, apply the patch and run "perl translate update" for any
translation. Check the revised po file and confirm that the new strings
are present. View the label batch edit page and confirm that the table
headings look correct: Tools -> Labels -> Manage batches -> Edit batch.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, passes all tests.
Similar fixes are probably needed for other pages of the labels
modules.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit e8f5ee9eef7a558ae1af8237493f8dc52e52945a)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>