Merge pull request #18 from eins78/master

markup: fix unlock (top) alert
index: sponsor durch vereinsinfos ersetzt
Merge branch 'master' of github.com:weimarnetz/web
site: add an Error 404 page

activate with:
`server.errorfile-prefix = "/srv/www/htdocs/errors/status-"`

as per <http://redmine.lighttpd.net/projects/lighttpd/wiki/Server_errorfile-prefixDetails>