Merge to ensure CrystalFieldFunction is available and up to date.

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

This reverts commit d07e2dcc.

When IPropertyManager::getValue fails to assign the property to the
specified type, a runtime_error is raised. Changed the error messages in
all (specific) cases to specify exactly what type it was expecting,
i.e. (const) shared_ptr<X> not just X or const X.

IPropertyManager::getValue has specialisations for shared_ptr<T>and
const shared_ptr<T> for most types. The only missing ones were
IFunction, TableWorkspace and WorkspaceSingleValue, and these have been
added.

Refs #9059

Refs #8983

Rename ISpectrum::maskSpectrum() to clearData() and remove option to set histogram data to a value other than zero as it was an inconsistency. Re #3378.

- Refs #3203: Implemented ISpectrum. It is the base class of EventList and Histogram and contains the spectrum number and list of detector IDs for a given spectrum.
- ISpectrum return X/Y/E vectors. EventList, e.g. calculates the histogram on the fly.
- Moved the EventWorkspace MRU list of histograms to be contained within the EventList; better code separation. Made a EventWorkspaceMRU class to encapsulate this more easily.
- Workspaces must implement getSpectrum (const/not const) to return a ISpectrum object. dataX(i), etc. methods on MatrixWorkspaces no longer need to be overridden since they call getSpectrum()
- Got rid of EventWorkspace::getEventListatPixelID() and doneLoadingData()
- replaceSpectraMap() methods offers backwards-compatibility with SpectraDetectorMaps by setting the specNo and detector list when called. Must be called AFTER creating all the spectra in a workspace.
- Refs #3318: maskWorkspaceIndex() implemented as part of ISpectrum.

Dx is stored in memory, but at no cost unless it's used. Re #2796.

Refs #2751: Added stub for Fake MD data algorithm. Made properties report the type they expected when you give the wrong value.