Follow-up from "Adapt to new UT channel ID and geometry"

The following discussion from !550 (merged) should be addressed:

• @sponce started a discussion: (+3 comments)

  These should be converted to new Histograms. They are not thread safe and would fail in multi-thread mode As @sponce suggested we need to move to Gaudi::Accumulators instead of AIDA::IHistogram*D as the later is not thread-safe, there are multiple instances of those in the UT code where we use those, a transition to Gaudi::Accumulators should be executed to close this issue. @ganowak : can you take a look , this should be easy as FT, VP already did this .. cc @xuyuan