Added basic AudioResourceManager, sound playback

Added basic AudioResourceManager, and sound playback.
TODO: music playback

    assets/sample.png -> assets/images/sample.png
    assets/audio.ogg  -> assets/sounds/audio.ogg

    src/audio/AudioPlayback.cpp        (+)
    src/audio/AudioPlayback.h          (+)
    src/audio/AudioResourceManager.cpp (+)
    src/audio/AudioResourceManager.h   (+)
    src/audio/MusicPlayer.cpp          (+)
    src/audio/MusicPlayer.h            (+)
    src/audio/MusicTrack.cpp           (+)
    src/audio/MusicTrack.h             (+)
    src/audio/SoundChunk.cpp           (+)
    src/audio/SoundChunk.h             (+)
    src/audio/SoundPlayer.cpp          (+)
    src/audio/SoundPlayer.h            (+)
    src/core/MainManager.cpp
    src/core/MainManager.h
    src/util/Asset.cpp                 (+)
    src/util/Asset.h                   (+)