add a super basic onboarding tutorial

[recluse4615]

there's a "tutorial" game (we will need to pregenerate a world, as the --gameid param doesn't really do anything in SP) that we can suggest new users try out on their first time launching.

it won't be persistent, it will be a lil' modal on first start up saying "hey! if you're new maybe you wanna try out this tutorial" and only if the user presses "yes" will:

• the latest versions of "tutorial" + MT will be downloaded
• the pregenerated world will be downloaded
• the game launched on the tutorial world

completely optional, but could help reduce a bit of friction for some users