[Android] Support http://w3c.github.io/manifest/ for packaging tool

This commit is just first step for https://crosswalk-project.org/jira/browse/XWALK-1919.
Support "start_url" and "xwalk_launch_screen" field in manifest.
The legacy field "app.launch.local_path" and "launch_screen"
are still supported, but will print a warning message.
should this `launch_path` also be deprecated?