Tournament entrants don't get dropped or otherwise marked when they decline

[EliAndrewC]

The tabletop tournaments app sends an SMS reminder asking people to text Y or N to confirm or drop out of the tournament.

We correctly handle the Y case but not the N case. We currently don't do anything when we receive a non-Y response.

We will need to decide how to handle edge cases such as what happens if someone replies with neither Y nor N or what if they reply with both, etc. The correct thing is probably to just display "nonstandard response" on the form and then let the admin see what text message they received, so they can decide whether to include the person. Ditto for if we receive multiple texts; we should probably just set their status to "nonstandard" and show the texts we received, or something.