Provide user access to implemented rulesets

This blueprint overlapped with the configurable-rules one. Now that the latter is implemented, this blueprint is refocused on the user side of the configurable rules feature.

The problem is to provide a way for players to choose the rules for the game to come. Note that in a future multi-players game, this means that all human players could vote or give a hint for their preferred ruleset. Also note that this blueprint does not cover the selection of individual rules, but of existing rulesets.

Original statement follows.

    Duo implements the classic Uno rules.
    But everywhere I play this game, local rules apply.
    For instance :
      - Cutting (if I have the exact same card, I don't have to wait my turn
        if I'm quick enough to play it before the next player)
      - Zero swapping : playing a Zero card allows to swap cards with any other player
      - +4 stacking : same rules as the +2.
    It would be great if users could create their own rules. Or if you could enable some as options.