[Android] Implement manifest parser and enable loadAppFromManifest().

1. The class XWalkManifestParser parses manifest.json and provides
   the url of target page, it also provides the permissions declared
   in manifest.json.
2. The method loadAppFromManifest() use XWalkManifestParser to get
   target url and permissions, and navigate to the target page with
   the permissions.
[Android] Implement permission control for accessing Cross-Origin URLs.

The class XWalkContent exposes the native method nativeSetPermissions()
to Java. When nativeSetPermissions() is called, the permissions declared
in manifest.json will be passed to render through IPC, then the allowed
url partterns in permissions list will be added to the WebKit security
policy white list.