Implement a tile copying method in large-scale tile coding

Implement a tile copying method in large-scale tile coding

A tile copy mode is introduced, while allows a tile to use
another tile's coded data directly at bitstream level. This
largely reduces the bit rate in this use case. Our tests
showed that 10% - 20% bit rate reduction was achieved.

Change-Id: Icf5ae00320e27193b15ce95297720f8b6f5e7fd9