Ignore large commits for certain metrics

[wschella]

Above certain thresholds in commit size, the lines committed should not count towards "total additions" and "total deletions" as it renders a sensible interpretation of the metric void. So these should not count, or these metrics should not be displayed at all.

[iasoon]

Determining this threshold is nontrivial and case-dependent (i.e. changes in data files are usually much larger than code changes). #additions is just a stupid metric, as is #commits, or #anything really. We display these because we haven't got anything better. This is why G2 is something that should happen.

[wschella]

pinging @timodw ^^^^^^

[timodw]

I follow @iasoon, will look further into this in september together with him.