Fix summary stats

This ought to make @mikewray happy!

Fix for [#151 on ka-lite-central](https://github.com/fle-internal/ka-lite-central/issues/151) which also was also appearing on distributed (so fixed here, and will trickle merge with central). 

Now we show summary stats correctly for all groups, not just the first one. 

@aronasorman should be a fairly low friction change, but would be good to have someone sanity check the code and test the views