WIP: Argparse reaction reference

[jonls]

Add specialized argparse type for reaction references. This type guards against using non-existing ID since the actual ID string can only be obtained (through resolve()) if the reaction is defined in the model. Currently requires a MetabolicModel which is not ideal for commands that otherwise don't require this model representation. This may have to wait for the work on restructuring NativeModel to be implemented in terms of that model representation instead.