windeployqt: Add translations.

Use lconvert to concatenate all required files
into one qt_XX.qm which is then loaded.
This way, the application loads the catalog file qt_XX.qm
when running against installed Qt and the concatenated file
containing only the required translations when deployed.

Change-Id: I3a5cf76705a23eee983ff5356107d40e399d6cc1
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>