This also has the added benefit that after a restart we don't get the
same random numbers all the time because we forgot to initialize the
RNG with srand().
This matches basically all other Spider implementations I've played,
and makes playing much easier :)
I have left click-to-reveal in place, but mostly incase there is a
condition I've forgotten about.
Scoring is designed to mimic Microsoft's implementation - starting at
500, decreasing by 1 every move, and increasing by 100 for every full
stack.
Fixes GH-5319.
