Released Google+ Online Battle!

Hi, I've released online battle feature through Google Play Service today! Please make sure to use WIFI connection for the best performance. It's working even through Phone Carrier's network such as Verizon or ATT but from my testing, it was really slow. In online battle, you can choose to play against "auto selected" player or a friend in Google+ circle through invitation. Note: unless they both link in Google+ circle, you won't get notified when other player sends an invitation.