Make Tutorial menu choice auto-start first *unsolved* tutorial scenario

[byorgey]

Choosing Tutorial from the main menu now automatically starts playing the first unsolved tutorial scenario, rather than always starting with the first. Closes #2308.

[xsebek]

I tested it, and it works well. 👍

I was worried about what it would do after you had solved all the scenarios:

# --autoplay, but counts as solution:
for s in data/scenarios/Tutorials/*.yaml; do cabal run swarm -- -i $s --run <(yq '.solution' $s); done

Once all are solved, only the first tutorial will open, like the current state.

[byorgey]

Once all are solved, only the first tutorial will open, like the current state.

Yes, that was on purpose: that is accomplished by the code firstUnsolved = (tutorials >>= find unsolved) <|> (tutorials >>= listToMaybe), which tries to find an unsolved tutorial, but if there isn't one (i.e. if tutorials >>= find unsolved results in Nothing) it falls back to tutorials >>= listToMaybe which takes the first element of the tutorials list.

Note that could still be Nothing if the tutorials list is empty --- see #2309.