Substantial reworking of code for arf and kf groups.
Substantial restructuring of the way we estimate the rate of decay in prediction quality and determine the arf interval and amount of boost used. Also other changes to support moving to a lower first pass Q which exposes some new features and allows us to better distinguish genuinely static blocks from low motion or noisy blocks. Net gains now visible on all the test sets with std-hd PSNR up 1.87%. There are still some bad outlier cases but most of these are low motion or slide show type content where the metrics are already high at any given rate. The best + case is up by more than 10%. Change-Id: I18e25170053bdf3188f493ff8062f48a74515815