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.