Bug 30373: Enable translation of UNIMARC frameworks

Bug 30373: Enable translation of UNIMARC frameworks

This patch adds a new translation file, *-installer-UNIMARC.po

To test:
1. On top of all previous patches
2. Apply this patch
3. Create (or update) some language
Ej.
    misc/translation/translate create xx-YY

    verify new file misc/translation/po/xx-YY-installer-UNIMARC.po
4. Install new language
    misc/translation/translate install xx-YY

    verify new dirs:
        installer/data/mysql/xx-YY/marcflavour/unimarc/{mandatory,optional}

5. Repeat install procedure selecting xx-YY language and UNIMARC
   verify all frameworks are present

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>