Made CMS file downloader python 2.7 compatible and tidied up command line
Made CMS file downloader python 2.7 compatible and tidied up command line

The rest of the ETL uses python 2.7, so fixed CMS downloader to no
longer require python3. Also, cleaned up the command line to no longer
request two file paths when only one was being used, and enabled
selection of the CMS file parts from the command line instead of having
them be hard-coded.

OHDSI/ETL-CMS,OHDSI/ETL-CMS