Set up Icinga-Web on/for Ubuntu

I tested and setup Icinga-Web for Ubuntu. I determined (or rather figured) that the Debian repository simply isn't compatible with Ubuntu due to dependency conflicts as I more or less already found out in #6.

On IRC I was suggested to use the packaging from debmon.org for Debian, but didn't feel comfortable changing that at the risk of breaking backwards compatibility. As far as I can see this PR provides full Backwards Compatibility, at the cost of having two unfortunate default values.