Disallow empty string as valid player name

[joshhting]

Right now, if we attempt an empty string, the text field shows a grayed out "Player 1" regardless of which player it's for. Also, the TA brought up the issue of players being able to have the same name. While this doesn't actually break our code because our players have unique player IDs, is this something we want to allow? I think there are valid arguments for both allowing and disallowing it.

[joshhting]

I think it's ok if we allow players having the same name, but I think we should at least disallow players from picking the same color.