Bug 26418: Fix translatability of REFUND credit type

Bug 26418: Fix translatability of REFUND credit type

The description of REFUND type accountline credits introduced with the "issue refund" feature is not translatable.

To test:
- Make sure a language with a complete translation is installed
- Switch to the language
- Go to any user account
- Add a manual invoice
- Pay it off fully or partially
- Click on "issue refund"
- Confirm the refund
- Check the description of the line in the patron account is not translated.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>