[Android] Support embedded mode in packaging tool.

Some developers want to package web app with independent
xwalk's runtime library, and don't care the size of it
too much.
    
Pacakaging tool would copy all the xwalk's runtime library
into target application package, which includes the
.so, .jar, .apk file etc. By default, packaging tool
uses shared mode for web application.
    
Sample Usage:
python make_apk.py --name=Intel --package=org.xwalk.example
--app-url=http://www.intel.com --mode=embedded
    
BUG=https://github.com/crosswalk-project/crosswalk/issues/765