Carry out a full licence evaluation of listings scraped and update links accordingly

[Pierre-VF]

Need to:

• review all underlying listings and their licences
• add licence of the listings in the associated TOML file (name, url, license)
• check that no listing needs to be excluded due to license reasons
• autogenerate credits on the frontend based upon updated info
• evaluate possibility of avoiding fulltext readmes in listings

For listing download:

• put all files in ZIP (and only keep a few of the files to make it lightweight), with included license statement
• update app code to download and unzip the file