rd: remove unnecessary mem copies
rd: modify recon generation in rd 0 to have lesser mem copies
rd: fix incorrect check for rdlevel

Merge-skip check should be only for rdlevel 2
rd: optimize rd 0
common: [OUTPUT CHANGES]: change default ratecontrol mode to CRF-28. AQ on
(strength 1.0), CUTree ON. SSIM reporting On, PSNR off.
encoder: increase precision, add ssim db info to csv output.