Be a little more careful with nearly-zero priors in optimizer
Fix execution order for ShapeletPsfApprox plugin
Use new Swig cast macro instead of a home-brew one
Doc fix for TruncatedGaussian
Fix indexing bug in MultiModel creation
Remove unused persistence from Prior classes
Add SoftenedLinearPrior class for differentiable flat priors
Snapshot from HSC fork of CModel classes, as of tag HSC-3.2.1

This commit is not expected to build, as it depends on
meas_extensions_multiShapelet, and we've already removed that from the .cfg.
Make OptimizerDisplay work with CModel
Minimal changes to get CModel compiling against LSST fork

Adapt to header file refactoring.
Remove inheritance from meas::algorithms::Algorithm.
Adapt to new exception names.
Switch to new ShapeletPsfApprox plugin from meas_extensions_multiShapelet
Switch CModel schema usage to version 1: FunctorKeys, '_' delimiter
Documentation improvements for CModel
Convert CModel to meas_base exceptions and method signatures.

Using MeasurementError also enabled a cleanup of the error-handling in
the determine*FitRegion methods, because we can now store which flag
to set in the exception instead of having an exception throw for one error
condition and a null return for the other.
Python plugins for CModel magnitudes.
Merge branch 'u/jbosch/DM-240'