Field member variable in HookeElasticity

[constantinemoseley]

Description
The field member variable in HookeElasticity is called "self.ref" but optimize.morpho searches for "self.field" .

Files
Bug is located at: morpho/modules/functionals.morpho:62
Optimizer searches at: morpho/modules/optimize.morpho:740

[softmattertheory]

Thanks for this @constantinemoseley — we need to have a think about what to do here. Currently the optimizer only looks in the Field property, but perhaps it should use introspection to look across properties.