Add introduction wizard

[with-heart]

I want to ensure that users understand what the app does and how to use it.

I also want to ensure that it's not annoying. If you've seen it before, you can skip it (instantly via auto-focus?).

• Why?
  • in-game "Random" is only random within the current match, not your entire match history
  • instead generate a random civ from a customizable list of civs
  • app guarantees that all civs see equal play
• What?
  • round-based civ randomizer
  • generate a random civ to start the round
  • mark it as played after your match
  • once played, a civ won't generate again until next round
  • round ends when all enabled civs have been played at least once since the beginning of the round
• How?
  • this part is subject to change since I'm still not happy with the UI for this, so I'll come back to it later (maybe)