Turn on global rotation-zoom warping prediction

Turn on global rotation-zoom warping prediction

With this patch, the ZEROMV mode is overloaded to represent
a single global dominant motion using one of three models:
1. True zero translation motion (as before)
2. A translation motion different from 0
3. A Rotation-zoom affine model where the predictor is warped
The actual model used is indicated at the frame level for
each reference frame.
A metric that computes the ratio of the error with a global
non-zero model to the error for zero motion, is used to
determine on the encoder side whether to use one of the two
non-zero models or not.

Change-Id: I1f3d235b8860e543191237024a89041ff3aad689