Updated Czech translation
Updated Spanish translation
Updated Slovenian translation
Updated Serbian translation
Updated Hungarian translation
Updated Czech translation
Add session description for Flashback mode with Compiz

This is _not_ a supported mode for Gnome Flashback.
We don't install these session files by default.

These files are here only as a convenience for our downstream Ubuntu,
to make it easier to collect translations for this session description.

Signed-off-by: Philipp Kaluza <floss@ghostroute.eu>
Bump version to 3.8.1

in preparation for release.