Importer: pass an enum class rather than a string to distinguish between a component and a units.
Importer: pass an enum class rather than a string to distinguish between a component and a units.

hsorby/libcellml,cellml/libcellml,hsorby/libcellml,nickerso/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,nickerso/libcellml,cellml/libcellml