We now signal joint strengths and use a greedy algorithm for the search.

low-latency, cpu-used=4:

ll4-cdef@2017-03-22T03:42:10.815Z -> ll4-cdef-newsearch-var-header-newlambda-refine4@2017-03-22T15:56:46.471Z

   PSNR | PSNR Cb | PSNR Cr | PSNR HVS |    SSIM | MS SSIM | CIEDE 2000
-0.0792 |  0.3551 |  0.4393 |  -0.0108 | -0.1338 | -0.0141 |     0.1452

Change-Id: I619ae1c7c7d7ec04fe993cabc5773b07c3f5b201