[Android] [Shared Core] Move implementation of org.xwalk.core into org.xwalk.core.internal

This is the very first step of implementing shared mode for xwalk core.
In future, the invoking between org.xwalk.core and org.xwalk.core.internal will use java reflection so that it can be both within and across packages.

The PR is quite large because of the whole folder moving. I suggest reviewers to review this __commit by commit__.

__Commit 1__: add a script to do the pure moving and renaming. Any change in org.xwalk.core will make this PR unmergable. In order to avoid this rebase nightmare, i introduce this script as the first commit.
__Commit 2__: pure moving and renaming, The whole change is generated by the script added in commit 1. If you agree with the logical of the script, this commit can be skipped for reviewing.
__Commit 3__: Remove the script
__Commit 3&4__: The real change that make sure everything works as original after the moving. Including:
1. add a thin wrapper in org.xwalk.core for upper layer of API to use.
2. adjust some embedders use internal classes to change package
3. adjust some paths in build and test system.
4. address the resource issue.

I've verified all test cases, cordova usage(needs patch in cordova repo) and app packaging tool usage. All works well. Suppose the PR will have quite a long review period and will meet conflict very often. I suggest to do the review first. If it's ok to go, i will do the rebase at last and verify all test cases again.

@yongsheng @sqiu, please help review.
@junmin for the app packcage tool, PTAL