Add horizontal and vertical scan order for 1-D transform

This commit enables the 1-D transform to use Manhattan grid vertical
and horizontal scan order for transform coefficient entropy coding.

Enabled in inter prediction mode, the hybrid 1D/2D transform coding
scheme outperforms the 2D-DCT based coding system used in VP9 by
lowres_all  1.7%
hdres_all   1.4%

As one coding option, in addition to the existing 17 other transform
types in ext-tx experiment, the 1D/2D hybrid transform improves
the coding gains:
lowres_all  2.2% -> 3.0%

Change-Id: I9cefa9d9e38224546d0afd67feecd9f8d4a16ab0