Make multiple roots model share the resources.

Make multiple roots model share the resources.

Previous code generate new refcounts per each scene roots.
If one model file has multiple roots, then each root didn't share there
resouces each other.

And also, due to the resource cache patch block multiple RawResouces loaded,
multiple roots scene was not works well.

This patch make we use only one refcounter per one model,
So we can assume that we only load just one times if
multi scene use same resources

Change-Id: I752f8a4ed352d4c328b1f48791bf0fee4fc8adcb
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>