*: use "Liberation Sans" explicitly in ODT printouts

When these printouts were made, cloudooo did not had so many fonts as
today, and it was picking up "Liberation Sans" for the "Arial" used in
these templates;

Since
nexedi/slapos@135cbe43
( yes, 5 years ago ) we have more fonts, and since then the rendering of
these printout changed, a "Roman" font was selected instead.

This changes the templates to use explicitly "Liberation Sans", which
makes the printouts use the old looks even on newer cloudooo .