Follow-up from "Add monitoring using global atomicity histograms"

The following discussion from !1186 (merged) should be addressed:

• @graven started a discussion: (+7 comments)

  this is a specific version of the generic code implemented here. Perhaps it would be better to re-use it (even if only to implement this code)

Other comments should also be addressed:

• use std::unique_ptr !1186 (comment 6675020)
• use std::make_unique instead of new !1186 (comment 6675021)
• add mass plot to DisplacedDiMuonLine
• !1256 (merged)
• add monitoring for velo tracks split by forward / backward direction
• !1257 (merged)
• turn on Drell Yan line monitoring (related to #432 (closed))
• !1257 (merged)
• wrap the device buffers in a class with the histogram descriptors as suggested by Roel !1186 (comment 6802459) and !1186 (comment 6802553) to avoid copy-paste errors