lighttpd: restart service if config changes

Using /etc/lighttpd.conf "hides" the config file from NixOS so that it
will not automatically restart the service when its config file changes.
So don't do that.
Merge branch 'lighttpd' of git://github.com/bjornfor/nixos into upstream-master

Moves config file into the store rather than polluting etc, which has a
number of benefits

Signed-off-by: Shea Levy <shea@shealevy.com>