1. It seems that many part of the system is upset about symlinks, revert to bind mounts
2. New system and vendor mirror implementation found, no need to copy anything
3. Thanks to the new mirror implementation, adding new items to /system and /vendor is now possible
4. Re-written some coding style
1. Remove stage 4 bind which mount files back, use symlinks instead
2. libs do not support symlink, make a copy to data if needed
3. Proper support for adding new files into /system/vendor on devices with separate vendor partition
