STYLE: Store only filenames in parameterFileList, not ("-p", file) pairs
STYLE: Store only filenames in parameterFileList, not ("-p", file) pairs

It appears redundant to store {"-p", filename} pairs in the local variable `parameterFileList`, instead of just the filenames.

This commit also avoids retrieving `argMap[ "-p" ]` multiple times for the same parameter file.

SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix,SuperElastix/elastix