add gpgs notification callback.
Merge branch 'master' of https://github.com/Wu-Hao/TankMultiplayer

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
Add show win or lose
remove main screen horse.
merge with wuhao, and add GPGSChecker.
Merge branch 'master' of https://github.com/Wu-Hao/TankMultiplayer

Conflicts:
	Classes/AppDelegate.cpp
	Classes/GameScene.cpp
	Classes/MainScreenScene.cpp
	proj.ios_mac/TankMultiplayer.xcodeproj/project.pbxproj
Merge pull request #25 from fusijie/master

merge with wuhao. v0.5