Bug 12020: Allow translating label-edit-batch hardcoded strings

Bug 12020: Allow translating label-edit-batch hardcoded strings

Move the hardcoded error strings in the batch label edit into the template,
so they can be translated.

Test plan:
1) Apply patch
2) Go to Home -> Tools -> Label edit
3) Create a new batch with some items in it
4) Try to trigger any of the errors, check that the error
   messages look correct
5) Update a language xx-YY
5) Check that the error messages show up in xx-YY-staff-prog.po

Signed-off-by: Pasi Kallinen <pasi.kallinen@joensuu.fi>
Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Changed branch to library in one of the error messages.

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>