Resolve "Unroll parameter list for FieldVector constructor"
This MR uses a template parameter pack (as it likely was intended) in the parameter_unrolled method of the ElasticMaterialBase class instead of a variadic function argument. This requires templating the function. The coordinates are then passed to the FieldVector constructor taking an initializer list as argument.
This, in turn, resolves the assertion error reported in #9 (closed).
Closes #9 (closed)