Elgg - Use symbolic link to simple cache directory

[JedMeister]

In Elgg by default we're enabling "simple cache". However to get the most advantage out of it a symlink /var/www/elgg/cache/ to /var/www/elgg-data/caches/views_simplecache/

I.e.:

ln -s /var/www/elgg-data/caches/views_simplecache /var/www/elgg/cache