Bug 24973: Load custom localization file

Bug 24973: Load custom localization file

It adds a new localization directory that could
host a custom SQL file for each language,
xx-YY/custom.sql

This will be the last file to be loaded at
install time, it can be used to set any difference
from default values.

It can't be deselected at install time.

Moved corresponding files for de-DE, it-IT,
nb-NO and completed es-ES

To test:
1) Apply the patch
2) Install es-ES/de-DE/it-IT/nb-NO translation (any lang)
   ( cd misc/translation; ./translate install es-ES )
3) Do a clean install using es-ES
4) After all files have been loaded check:
    * A new section labeled "Localization data added"
      with one file, custom.sql
    * Inspect the value of FrameworksLoaded syspref,
      last entry must be custom.sql
5) Remove/rename the file or localization dir and
   repeat 3/4, install must proceed normally

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>