Use single definition for the bvparmYYYY.cif string.

And update to the actual data file used.
Improve representation for blank BVParam().
Export all wrapped ScatteringFactorTable classes.
Small docstring updates.
Fix Python override of PeakProfile.ticker().

Also add unit test for ticker method override.
Fix Python override of PairQuantity.ticker().

Also add unit test for ticker method override.
Fix Python override of PeakWidthModel.ticker().

Also add unit test for ticker method override.
Wrap ScatteringFactorTable::ticker() method.

And also add unit test for Python ticker override.
Register CovalentRadiiTable on import of overlapcalculator.