Flatpak support for prism

[Antonello]

Hi, 

I wrote a simple flatpak manifest to allow using prism on any linux machine without worrying about dependencies, currently targets version 4.9. 

It seems to work well for now, I've been using to run my uni projects.

Idk if there is a better place to put this or if it would make sense to make a pr on github, I'm open to suggestions.

https://github.com/adettori/prism-flatpak/tree/flatpak

(It's a bit messy but it works :) )

Hope this helps other linux users and looking forward to hearing any feedback!