feature: when a new match is started, stop the previous match if in the past

[iamgiolaga]

Bug Report

What

If you successfully complete a match, you need to stop the match in order to create a new game.
When users use /start, we should check if there's already existing match and, if that is in the past, we should directly stop the previous one and start a new match.

How to replicate it

no matter what happens, if you use /start with an existing game, it always returns the existing game

Additional Note

challenge: this feature is doable if the user inserts a valid date / time, but if not, we can't compute if the game is in the past. Same for the format, which format should we use to parse day and time?

[iamgiolaga]

update: problem would be simplified if we implement #35 first