FIX: regularly update scenario texts on clients if scenario window open

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6256 8aca7d54-2c30-db11-9de9-000461428c89
FIX: always use cached scenario texts

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6257 8aca7d54-2c30-db11-9de9-000461428c89