Generalize quantizer setup so that quantization and TX can use
different coefficient shifts/scalings without inpacting RDO lambda
generation.

This patch is documentaiton + a minor refactor setting up later
work; it causes no functional change.

monty-daalaTX-fulltest-Daalabaseline-o1f@2017-11-07T00:01:20.779Z ->
 monty-daalaTX-fulltest-DaalaRDO-o1f@2017-11-07T00:02:31.347Z

PSNR | PSNR Cb | PSNR Cr | PSNR HVS | SSIM | MS SSIM | CIEDE 2000
 N/A |  0.0000 |  0.0000 |      N/A |  N/A |     N/A |        N/A
(note-- the numbers above were collected using --cpu-used=3, which
 appears to be newly broken.)

monty-daalaTX-fulltest-Daalabaseline-o1f4@2017-11-07T05:59:16.553Z ->
 monty-daalaTX-fulltest-DaalaRDO-o1f4@2017-11-07T05:59:50.180Z

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0000 |  0.0000 |  0.0000 |   0.0000 | 0.0000 |  0.0000 |     0.0000

monty-daalaTX-fulltest-Daalabaseline-s1@2017-11-07T00:01:46.582Z ->
 monty-daalaTX-fulltest-DaalaRDO-s1@2017-11-07T00:02:56.282Z

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0000 |  0.0000 |  0.0000 |   0.0000 | 0.0000 |  0.0000 |     0.0000

Change-Id: Ia5a3c052eacd17184ca1b0fe6d032cfb9afdb77f