Return 404 when version/mod not found, instead of 500
Return 404 when version/mod not found, instead of 500

Also write more useful request info for the sever log instead of just
the traceback.

KillerKiwiJuice/planetary-annihilation-db,speth/planetary-annihilation-db,KillerKiwiJuice/planetary-annihilation-db,speth/planetary-annihilation-db