cross eval methodology

[sethtroisi]

Per offline discussion around sethtroisi#4 and https://cloudygo.com/all-eval-graphs?bucket=cross-eval

Andrew suggested

• Removing all models below the "knee" (e.g. model 200)

Seth mentioned

• Completely removing ratings.py and all that rsync jazz
• Add a models cloud bigtable table with models and runs ([oneoff] Script to push models to a new bigtable models table #797)
• clean up cross-eval panel/model selection.
• Figure out how to correctly tag run (e.g. v15) in cbt

[sethtroisi]

• Fix length mismatch between cc eval and backfill (they are both strings instead of ints now)