Dominoes - now with a second level

Puzzle #2 is coded and is working.

I started making a JSON parser to construct the puzzle configuration, but at this point, it's just about as easy to do it by hand. Ugh.

I'm not certain there's a unique solution to Puzzle #2. That's a corner I'm willing to cut for the time being.

I dumped out a bunch of dominoes on my desk and I formed the designs for 5 puzzles, plus the trivial one that I started with. 6 puzzles, that seems like enough to call it a game.

There currently isn't a way to navigate between puzzles - that'll come soon, I expect.