[Android] Implement runtime client with runtime library embedded

We should support both shared and embedded mode for runtime
client to use runtime library, which providing java class, native
lib and pak resources for runtime client.

Currently, only shared mode is implemented. In shared mode,
runtime library is an Android app.

This commit implements an alternative to allow packing runtime lib
embedded in runtime client. The api will stay unchanged and the
client of runtimeView will not aware the difference.

Add a new target, xwalk_runtime_client_embedded_shell, which is
the shell using runtime view with library embeded. It's for
testing purpose.

TODO=https://github.com/crosswalk-project/crosswalk/issues/657
BUG=https://github.com/crosswalk-project/crosswalk/issues/640
[Android] Pack the files embed mode needs into app template

To create an app using embed mode of runtime library.
It needs the relevant java class, native library and assets.

Copy them in target prepare_xwalk_app_template so that
they will included in generated tarball of app template.

BUG=https://github.com/crosswalk-project/crosswalk/issues/657