Merge to ensure CrystalFieldFunction is available and up to date.

This uses the -fix option on clang-tidy to automatically fix all
the unused usings declarations that have crept into Mantid.

Also fix a memory leak in a unit test.

Workspace2D and EventWorkspace both initialize HistogramData::Histogram
in their init() methods. Previously this was written in a suboptimal way
that caused more shared_ptr access (atomic increment/decrement
operations) and memory allocations than necessary. The improvements here
may give speedups on the percent level.

Mechanism similar to what we do for SpectrumDefinitions in
Beamline::SpectrumInfo.

This reverts commit d07e2dcc.

TOF 0.0 may not make sense (maybe ok for bin edges, but if the workspace
holds points...).