[Android] Remove hidden assets('.*', '_*') from ANDROID_AAPT_IGNORE pattern.

This patch will remove the ".*" and "_*" from the default exclude list,
and thus "hidden" assets will now be included in your assets
directory inside your .APK.

BUG=https://github.com/crosswalk-project/crosswalk/issues/631
Merge pull request #647 from junmin-zhu/dir

[Android] Remove hidden assets('.*', '_*') from ANDROID_AAPT_IGNORE.