Make content public

[kusma]

There's a lot of files that are stored on content.pouet.net, that doesn't seem to be publicly available (unless we'd brute-force crawl all files from that server, which doesn't seem good).

For Pouët 0.9, this was solved this way, and we should probably do the same here, if it's going to be viable for others to contribute for instance CSS changes.

[kusma]

BTW, I get that there's content that kinda "belongs" to the database, so it might not make sense for those to be put in the main repo. But normal CSS files and graphics assets (not counting user-submitted ones) probably should live here.

[lra]

I made it available: https://github.com/pouetnet/pouet-content But I agree that we should move those static files back into the main pouet-www repo.