[Android] Update xwalk_app_template after shared layer move into core

The main changes are:
1. There is no xwalk_runtime_java.jar any more.
2. Split xwalk_core_library_java.jar into app part and library part
   to support shared mode.
For aar package, since it on accepts one classes.jar, still create
xwalk_core_library_java.jar and pass it as argument when creating
aar package.

BUG=https://crosswalk-project.org/jira/browse/XWALK-2537
Yes, lgtm after that. Don't worry too much about the branch date, though: if there are outstanding issues we can just delay branching.