minor corrections, null checks, Message Class

-A few spelling corrections
-Null check added to Player such that if any param==null, it will not
initialize. perhaps an exception should be thrown?
-Message Class added. I know we didn't really discuss, but I am
envisioning it as simply being handed to the client, where it will test
to see if there are any cards, buttons to be shown, and then generate
the appropriate HTML....what are you guys thinking?