Cmake template improvements

[JonnyPtn]

Some things I find myself repeatedly doing whenever I start a new project with xygine, and figured would be useful to add to the template:

• Include files are part added to the project correctly
• Implemented a template state class
• Changed include guards to #pragma once

[fallahn]

Thanks! The only comment I might make is that MyFirstState is something I'd probably end up renaming when creating a new project, undoing some of the usefulness. That being said I don't have a much better suggestion other than perhaps DefaultState ..? Either way the only reason I've not merged this is the fact that it fails the CI - and I think it's an issue with travis rather than the code itself, so I'm waiting to see if it gets resolved.

[JonnyPtn]

Yeah I always rename it too, it's more useful to save me having to remember which functions I need/want to overload

hat apt-get error on travis is usually just some odd hiccup. I've restarted the build which should solve it, let's see... Travis builds now