Replace 8x16 lapping filter with a V matrix with a determinant of one.

The prior factorizations give perfect reconstruction in only the forward
 direction: post(pre(image)) = image, but are not sufficient to make
 prediction for static scenes instantly convergent.
For that we need pre(post(image)) = image as well, which can be achieved by
 having a determinant of one.

Also retrains the intra-predictors.
Remove FASTSSIM metric from bd_rate and rd_plot.

It is generally agreed that the FASTSSIM metric is currently not producing
 meaningful output, see issue here:

https://review.xiph.org/207/

It may make more sense to use when the scalar quantization is using proper
 quantization matrices and we may turn it on again then.
Update png2y4m.sh to use correct chroma siting.

When converting to y4m we should use 420jpeg chroma siting to avoid
 resampling chroma by a half sample in the encoder.