Add match validation

[tandrewnichols]

We need more validation around adding a match. Currently, you add matches in which individual games are ties, or even the entire match is a tie. For instance, you can enter the default scores, 11 to 11 in both games, and it works fine.

We should check that:

1. One player wins two of the games.
2. One player does NOT win three games (could affect ratings strangely).
3. The scores in all games are different.
4. Winning score is 11 if losing score is 9 or less.
5. Winning score is NEVER less than 11.
6. Losing score is AT LEAST 2 less than the winning score.

Mongoose has something called statics, so we could just add these to the match schema. I would like to see us, generally, move more of the logic to the schemas, since we're really doing operations against Matches and Players most of the time.

Something like:

Match.statics.validateGame = function(matchObj){
    // Do validation
}

Match.statics.validateMatch = function(matchObj){
    // Do validation
}

etc...