Ability to show cards with different layouts

[mfgea]

Description

Right now the cards are only shown in a column based layout. It would be nice to be able to, for example, show an expandable/collapsable block of cards.

Motivation

As we were going through a pretty standard column set (good/to improve/action items) we focused a big part of the retro on the 'to improve' column, that contained about 20 cards. We had to keep scrolling up and down to see cards, vote and rearrange them. It would have been a lot more comfortable to be able to collapse the 'good' column and see a block of 'to improve' cards (something like 5 cards per row).