Install Linux dist files

[abouvier]

Automatically install the files from #395.

[DanielGibson]

@Eonfge as you added those files, do you have an opinion about these changes?

Apart from that, I never tried using make install or similar with dhewm3, does it work as expected for the other files (executables and game libs)?

[Eonfge]

That would be great! I kind of forgot about it, so it's cool to see @abouvier pick up the slack.

My only remark would it, is that it would be extra cool if CMAKE could also update the metainfo.xml so it has an updated list of releases. Not sure how feasible that is though... perhaps it's easier to do it manually.