Download cover art on demand

[mborgerson]

It would be neat to see LithiumX support pulling cover art when it discovers an executable, on demand when the Xbox is connected the Internet, like the xemu website does. I may implement it sometime, unless someone beats me to it.

I've recently migrated out the metadata database built for xemu to have its own home at http://xdb.fyi, which would be a great source for title metadata and covers.