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)