[Android] Use loadAppFromManifest if a manifest.json is used for a web app

Add loadAppFromManifest support for web app. If web app is packaged with
manifest, directly use loadAppFromManifest API to load app.
Because native manifest parser only supports original proposal
"app:launch:local_path", manifest related test cases are modified.
When the specfication for manifest is stable, will revisit these test
cases and native manifest parser.

BUG=https://crosswalk-project.org/jira/browse/XWALK-100?filter=10007