Workaround the two remaining issues, mostly fixing the “load deck”
screen in tab_game:
 * Only preload up to the first 300 cards of a deck;
 * don’t even bother trying to load card images if they’ll be shown
with width <= 10

Trying a 17k cards deck like the one proposed in #67 is still a no go,
mostly due to the cpu time used to create all the objects. Anyway, i
tested decks up to 8k cards and they works fine now (if you like to
wait while trice is loading them)..