Jointly coding gain/theta/noref on P-frames

video1-short results:
non-robust:
           RATE (%)  DSNR (dB)
    PSNR -0.35052  0.01787
 PSNRHVS -0.40397  0.03273
    SSIM -0.38161  0.01849
FASTSSIM -0.36484  0.02334

robust:
           RATE (%)  DSNR (dB)
    PSNR -1.85044  0.10021
 PSNRHVS -2.16841  0.17816
    SSIM -1.93902  0.09961
FASTSSIM -1.98467  0.13023
Change ordering of CfL flip flag so that it's encoder just after use.

This will allow us to do joint noref/gain/theta coding on keyframes
Using joint noref/gain/theta coding for keyframes too

subset1 results:
           RATE (%) DSNR (dB)
    PSNR -0.481762 0.0305003
 PSNRHVS -0.743942 0.0449025
    SSIM -0.56423 0.0312397
FASTSSIM -1.25077 0.0409497
Implements skip_rest flag on the first band

Reduces the total number of symbols we have to code

video1-short:
           RATE (%)  DSNR (dB)
    PSNR -0.08130  0.00415
 PSNRHVS -0.07577  0.00561
    SSIM -0.06396  0.00291
FASTSSIM -0.12767  0.00727

subset1:
           RATE (%) DSNR (dB)
    PSNR 0.0163635 -0.000926524
 PSNRHVS 0.0184024 -0.00105508
    SSIM 0.0174851 -0.000821658
FASTSSIM 0.0242243 -0.000776809
Defining skip as theta=-1 for keyframes since it's much more common

subset1:
           RATE (%) DSNR (dB)
    PSNR -0.375649 0.0213739
 PSNRHVS -0.433576 0.0292169
    SSIM -0.3784 0.0173524
FASTSSIM -0.446371 0.0144125

video1-short:
           RATE (%)  DSNR (dB)
    PSNR -0.01509  0.00077
 PSNRHVS -0.01745  0.00129
    SSIM -0.01507  0.00068
FASTSSIM -0.01611  0.00092
fixes for issue 512
Tunes CfL for 4x4 blocks and compensate for TF scaling

subset1 results
luma:
    PSNR -0.134846 0.00708469
 PSNRHVS -0.0827634 0.00606356
    SSIM -0.132282 0.00536598
FASTSSIM -0.0761702 0.00245465
Cb:
    PSNR -0.984953 0.0338204
 PSNRHVS -0.322431 0.015904
    SSIM -1.00691 0.0268581
FASTSSIM -0.594378 0.0124368
Cr:
    PSNR -0.496393 0.0232284
 PSNRHVS -0.20442 0.0117632
    SSIM -0.577023 0.0201109
FASTSSIM -0.608689 0.01373