Adds icons for the substitution button.

I don't know if this is the right way to do this. The icon is a google
icon. Why isn't it included in the sdk?
Adds fab for doing subs and a top card.

My apologies for unrelated changes in a single commit. The fab should
have been a different commit. The top card is temporary. I think that I
want to use a single card that animates when a sub is picked and
executed.
Reinstates evenly weighted rows and moves positions to the bottom of each row.

I moved everything to the bottom because I assume that will be best for
when I'm having cards extend upwards to indicate incoming subs.