Various overhauls of the packs + automatic loading

Packs are now automatically loaded from the packs dir. Watermarks are
now supported with a format change. Playing multiple cards now works
correctly.
Add new packs from PYX.

Packs can be found at
https://raw.github.com/ajanata/PretendYoureXyzzy/master/cah_cards.sql.

I dumped it with a horrible python script.