cli should take as optional input parameter the location of the csv files from ystaf

[tngTUDOR]

Current:

prior to installing the package, the user must download by hand the csv files, and place them under ystafdb/ystafdb/data (only a few of them are required, see the install instructions for the specific list)

Expected

The user should be able to point to a directory where the csv files are located, like:

ystafdb-cli -i unzipped_directory regenerate output

if the user doesn't provide the -i option to the cli, then the (current) default location will be tried.

[tngTUDOR]

implemented as of v0_5