create ParticleCut process

This Process (ProcessCut to remove particles) occurs as copy in several examples. To avoid code duplication the correct way would be to move it into a separate class file under /Processes/

The following discussion from !91 (merged) should be addressed:

@dbaack started a discussion: (+3 comments)

When this Process is used in all 3 examples maybe it would be useful to move it to /Processes/

Edited May 05, 2019 by Felix Riehn

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