CHG: (An_dz) button offsets also to left and right

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7328 8aca7d54-2c30-db11-9de9-000461428c89
CHG: (An_dz) Skinable toolbar backgrounds

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@7329 8aca7d54-2c30-db11-9de9-000461428c89