增加scene定义，和reset按钮，添加ball的反弹系数和摩擦系数
#	modified:   Classes/AppDelegate.cpp
#	modified:   Classes/Box2dLayer.cpp
#	modified:   Classes/HelloWorldScene.cpp
#	modified:   Classes/HelloWorldScene.h
#	new file:   Resources/ResetNormal.png
#	new file:   Resources/ResetSelected.png
增加重力传感器处理，重力方向随手机方向调整
#	modified:   Classes/Box2dLayer.cpp
#	modified:   Classes/Box2dLayer.h
#	modified:   Resources/ball.png
#	deleted:    proj.android/assets/CloseNormal-1.png
#	deleted:    proj.android/assets/CloseSelected-1.png
#	deleted:    proj.android/assets/HelloWorld-1.png
#	new file:   proj.android/assets/ResetNormal.png
#	new file:   proj.android/assets/ResetSelected.png
#	new file:   proj.android/assets/ball.png
#	modified:   proj.android/jni/Android.mk
#	modified:   proj.android/jni/Application.mk
#	modified:   proj.android/libs/armeabi/libgame.so