Adding php5-json, apache config in sites-available

- Adding pph5-json to the dependencies. In debian, php5-json is a virtual package provided by php5-common, so it does not need to be installed explicitely. However, it probably doesn't hurt to do it, so we can add it to the installation command line for other distributions.

- I would rather edit in sites-available but no big deal, sites-enabled is just a symlink to it.

See discussion here: http://openenergymonitor.org/emon/node/2502