add cache header to vhost and media format cache
update nginx expires header example
delete vhost file add link to extends vhosts
Update README.md
Merge branch 'develop' of github.com:sulu-cmf/sulu-standard into feature/cache-headers
Merge branch 'feature/cache-headers' of github.com:sulu-cmf/sulu-standard into feature/cache-headers
Merge pull request #335 from sulu-cmf/feature/cache-headers

[FEATURE] add cache header to vhost and media format cache