relax SVN archive

The function has been added to the files 'model_free.py' and 'jw_mapping.py' in the 'specific_fns'
directory, and has been made accessible in the specific setup file. The purpose of the function is,
when supplied the data type, to return a string formatted in Grace's typesetting syntax. That way
parameter names can be displayed on the Grace axes as Greek text, superscript, subscript, italics,
or any other Grace format.

The file 'specific_fns/jw_mapping.py' has also had the 'return_data_name' function expanded to
include the spectral densities themselves.