[Android] Implement runtime client with runtime library embedded

Originally, runtime client relies on runtime lib, which is an
Android app as library providing java class, native lib and pak
resources.
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