Cluster summary rewrite

The ClusterSummary and ClusterSummaryProducer classes were updated to improve performance, as documented here:

https://its.cern.ch/jira/browse/CMSTRACK-51
(https://indico.cern.ch/event/322710/session/5/contribution/2/material/slides/1.pdf)
I think this sortMod is kind of pointless.

```
int iM = -1;
for (auto m : modules){++iM; if (m==mod) break;}
```
will likely be even faster