Add class for tracking modification event times.
Add EventTicker to the PeakWidthModel classes.

PeakWidthModel class now has public attribute mticker.
The ticker is clicked on any modification or when PeakWidthModel is
reassigned to another PeakWidthModelOwner class.
Add ticker() method to access PeakWidthModel ticker.
Implement ticker for PeakProfile updates.

Also add ticker() method for accessing the PeakProfile state ticker.
Implement ticker for ScatteringFactorTable updates.

Also add ticker() method for accessing the ScatteringFactorTable state ticker.
Implement ticker for tracking PairQuantity config.

Also add ticker() method for obtaining the PairQuantity ticker object.
The ticker object is updated whenever PairQuantity configuration
changes.  For the base PairQuantity class it is clicked on changes of
rmin or rmax.
Implement ticker for tracking PDFCalculator config.

Overload the ticker() method for obtaining the ticker of the last update
of PDFCalculator configuration or any of its composite objects such as
PeakWidthModel or ScatteringFactorTable.
Use PQEvaluator value ticker to trigger full calculation.

PQEvaluator objects now contain mvalue_ticker, which is clicked in
updateValue.  If the configuration ticker in the updated PairQuantity
is later, perform full evaluation instead of fast update.

Remove PQEvaluator::uncache() and PairQuantity::clearEvaluatorCache()
methods.
Implement serialization for EventTicker.

Also make fast updates in PQEvaluator require the value to be newer
than the PairQuantity configuration.
Implement serialization for PQEvaluatorOptimized.
Serialize ticker data in the tracked instances.
Implement getRDF, getRDFperR for DebyePDFCalculator.

F(Q) in DebyePDFCalculator is now always evaluated from qmin=0,
but the qmin cutoff is applied only when converting to the PDF.
RDF and RDFperR can be easily calculated from uncut F(Q).
Implement ticker for tracking BaseDebyeSum config.

Overload the ticker() method for obtaining the ticker of the last update
of BaseDebyeSum configuration or its PeakWidthModel composite object.
Implement ticker for DebyePDFCalculator config.

Overload the ticker() method for obtaining the ticker of the parent
BaseDebyeSum class and of the owned ScatteringFactorTable object.
Add PairQuantity method getEvaluatorTypeUsed().

Added public PQEvaluator::typeintused method.  Also added NONE
to the possible list of PQEvaluatorType.
Store StructureDifferenceMethod in StructureDifference.

The method of obtaining structure difference is now saved in
the StructureDifference.diffmethod attribute, it has nothing to do
in the AtomicStructureAdapter class.
Support OPTIMIZED evaluation for DebyePDFCalculator.

Also added tests and tests for modifying DebyePDFCalculator
configuration.
Test evaluator choice for changes in delta1, delta2.