Leaderboard styling

re: #28  The previous attempt:

> A couple niggling issues:
> 
> * Rows don't move until *after* firebase gets back to us. Feels really laggy. Admittedly, that may
  only matter for the debugging behavior.
> 
> * Reordering multiple focus rows looks pretty bad (overlapping shadows, too much movement to track).
> 
> * The bounce animation doesn't work on the first change to a row. Haven't been able to track down why.
> 
> * Rank fading/restoring feels awkward.