Extend MCParticle-Calorimeter Associations

[ruse-traveler]

Briefly, what does this PR introduce?

This PR modifies the logic of the existing MCParticle-Cluster associations. Previously, clusters were associated to only the 1st particle contributing, regardless of energy, status, or origin. If accepted, this change will now create associations between a cluster and all particles which initiated a shower in the calorimeter that contributed to the cluster.

What kind of change does this PR introduce?

• [X] Bug fix (issue #899 )
• [ ] New feature (issue #__)
• [ ] Documentation update
• [ ] Other: __

Please check if this PR fulfills the following:

• [ ] Tests for the changes have been added
• [ ] Documentation has been added / updated
• [X] Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No.

Does this PR change default behavior?

Yes.

[ruse-traveler]

Closing this down in favor of #1396 .