Bug 8347 - Koha forces UNIMARC 100 field code language to 'fre'

Bug 8347 - Koha forces UNIMARC 100 field code language to 'fre'

Changed Charset.pm to use defaultlanguage instead of 'fre'.

Signed-off-by: Rolando Isodoro <rolando.isidoro@gmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script.

1) Check system preference was added correctly:
   UNIMARCField100Language
2) Change code in preference to be not 'fre'.
3) Catalog a bibliographic record.
  - check plugin shows new value
  - check empty field is filled with new value from the plugin
  - check you can still edit it to be something else

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>