[TASK] Change XLIFF to version 1.2

In order to be able to use Qt Linguist to easily translate
XLIFF files, one has to use version 1.2 and reference the
corresponding XML namespace.

Qt Linguist may be downloaded from:
http://qt-apps.org/content/show.php/Qt+Linguist+Download?content=89360

Change-Id: I3a680428c313b199cc815d5d7abdf666ab547016
Reviewed-on: https://review.typo3.org/26974
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers