[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: I54a6a7ab03e5c27b7d641d1b636e2ffd603922bf
Reviewed-on: https://review.typo3.org/26972
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers