Changes row animation to be prettier and fixes nested StatsItems

Closes #93 

This PR resolves two items - the reload animation for nested items & handling multiple levels of nested items.

StatsGroup was modified to use recursion to dive into the StatsItems it contains.  The reload animation was updated to only add or remove (not both) the rows that are being hidden or expanded.  This ends up making a much smoother animation.

cc: @koke