bugfix for pixel clustershape filter, and, change HI tracking low-pt seeding from triplet to track

As listed in the commits, first commit is for bugfixing the clustershape filter, removing conflict between two vs three argument version of the operator(). This was a prerequisite for the update of low-pt tracking.

In the second commit, the HI tracking uses tracks instead of triplets in seeding, which is a significant improvement in timing. Details in: https://indico.cern.ch/event/345510/contribution/5/material/slides/0.pdf

This PR requires https://github.com/cms-sw/cmssw/pull/6374 to be merged, in order to run the full HI reco sequence successfully.


Should also the value of useClusterShape parameter be checked (in addition of its existence)?