Hierarchical rdmult scaling when tune=ssim

Hierarchical rdmult scaling when tune=ssim

Use different lagrangian multiplier scaling factor for different block
size. The blocks whose sizes are less than 16x16 share the same multiplier
of their parent block.

The additional gains/loss on top of the tune=ssim are:
Data Set   Overall PSNR   SSIM    MS-SSIM
Lowres         2.918     -3.691   -2.596
Midres         1.708     -2.656   -2.624
HDres          1.619     -2.496   -2.391
Midres_10bd    1.518     -3.263   -3.561

The overall gains/loss comparing to tune=psnr are:
Data Set   Overall PSNR   SSIM    MS-SSIM
Lowres         5.583     -6.208   -4.978
Midres         4.024     -5.610   -6.411
HDres          4.102     -6.614   -7.457
Midres_10bd    4.647     -7.181   -8.614

Change-Id: I0e6c5008488734e979b2dacde9fc2a17f3aa620f