Handle games with missing data

[roygutg]

Following #50, we know that data is downloaded correctly from RedMetrics1, and can detect cases where some shapes are missing nonetheless.

What to do when we find a game with missing data?
Our current idea is to filter such games out, at the FeatureExtractor level. Meaning, add a new soft-filter to do this. The exclusions table will show an informative reason, e.g. "incomplete data (non-neighboring consecutive shapes)"

[roygutg]

Based on the fact that in 798 arbitrary games (test sets 1-5), only 7 games had missing data, Yuval approved filtering such games out.