[Android] Support embedded mode in packaging tool.

Web application packaged with embed mode would own
independent xwalk's runtime library, which include the
.so, .jar, .apk file etc. This mode would enlarge the
size of web application.

By default, packaging tool uses shared mode for
web application.

Sample Usage:
python make_apk.py --name=Intel --package=org.xwalk.example
--app-url=http://www.intel.com --mode=embedded

BUG=https://github.com/crosswalk-project/crosswalk/issues/765