Added test assets

Added test assets
    assets/audio.ogg  (+)
    assets/sample.png (+)
Added build files for bullet library

Added build files for bullet library
    android/initialize_project.sh
    android/jni/bullet-setup/Android.mk   (+)
Added test example with bullet useage

Added test example with bullet useage
    android/jni/Application.mk
    android/src/org/libsdl/app/SDLActivity.java
    src/Android.mk
    src/main.cpp