first version of join() -- to be replaced

first version of join() -- to be replaced

this version is very suboptimal. we shouldn't take from longest piles,
as that will rip apart already constructed piles. instead, take from
piles where the card we want to move has the least amount of movable
cards _above_ it. even better if the card above is closed. even better
yet if there is no card above (resulting in an empty pile)