Config

Remove the hard coded configuration for Hadoop and put it into systemd inspired config and xml using `$` prefix templating. This addresses issue #1. The advantage, of course, is that customizations can be implemented trivially by users by making their own config directory and changing the settings as they see fit. We can also support other software more easily. e.g. Spark.

A lot of code was removed and replaced with config.

This PR doesn't contain a fully functioning screen client (yet) but as it's a lot of changes, I feel it's best to get this in sooner (ha!) rather than later.

Thanks.
`main` doesn't return an exitcode; this makes no sense