Minor changes

- Changed the ```worker_connections``` from 1024 to 5120 to increase the concurrency of the nginx proxy.
- Indented the ```nginx.conf``` (with 4 space tab indent)
- Added a ```client_max_body_size``` of 200megabyte. The reason why this was done, was because the default nginx upload size is 1 megabyte, which means many upload forms didn't work.
- Removing the ```X-Powered-By``` header from the backend, so end-users won't see which PHP version we're using.
- Adding 2 comments, telling how to provide the cache-control and expires headers from the backend. (e.g. ```.htaccess```)
- Install tmpwatch on installation. Some servers don't come with tmpwatch installed by default, this will result in a full tmp folder at some point. So now we make sure that the nginx cache temp folder will be cleaned.