Extend lowPt egamma modifier to conversions

[stahlleiton]

PR description:

This PR extends the egamma lowPt modifier (used in the UPC reconstruction) to conversions, lowering the super cluster ET threshold to 1.0 GeV for conversions as done for photons and electrons. In addition, it also reduce the thresholds of reducedEgamma collection used in MiniAOD to keep the low pT egamma objects.

@mandrenguyen

PR validation:

runTheMatrix.py -l 180,180.1,181,181.1

If this PR is a backport please specify the original PR and why you need to backport that PR. If this PR will be backported please specify to which release cycle the backport is meant for:

To be backported to 14_1_X