Integration manifest parser with app build tools.

1. Add "--manifest=/path/to/manifest/file" support in make_apk.py
2. Adjust the icon API in the manifest parser, it shoud provide all
   information of the icon from the manifest.
3. Fix the icon path incorrect issue for "--icon" option.
4. Add unit test for make_apk.py, run it through following steps:
   * Switch to the outside of "src" directory.
   * Run the command "python src/xwalk/app/tools/android/make_apk_test.py
     --build-dir=src/out --target=Release"