Build script to build web apps

    Build script to build web apps
    1: Add common build script make_webapp.py for both android and tizen.
    2: Add android build script android/android_build_app.py.
    
    Scenario:
    1: Find all the available web apps (Which contains manifest.json).
    2: Init update all web apps.
    3: Check whether build script exists, if no,
       hook the downloader download the specified version.
    4: Loop all the apps.
    5: Copy manifest.json to [WebApp]/src.
    6: Build with build script.
    7: Remove manifest.json.
    8: Move the build result to out folder.
    
    How to use:
    Build all apps for both Tizen and Android
        python make_webapp.py
    Build specified app
        python make_webapp.py --app=MemoryGame
    Only build for Android
        python make_webapp.py --target=android
    Update Web Apps and then build all of them
        python make_webapp.py -u
    
    The build result will be under out directory.