(kierongreen) ADD: double heights (slopes), different water levels per tile, and per tile climates

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6530 8aca7d54-2c30-db11-9de9-000461428c89
CODE: waterheight is sint8

git-svn-id: svn://tron.homeunix.org/simutrans/simutrans/trunk@6531 8aca7d54-2c30-db11-9de9-000461428c89