redirect to download adjusted

[BeritJanssen]

This branch

• adds a url argument to the download path, so that FDA / AuToDI data are downloaded selectively
• empties the respective output folders after zipping the download output
• removes the defunct burger menu from base.html
• removes the download link from the navbar (without 'FDA / AuToDI', it doesn't work, and the folders will be empty in most cases)
• redirects the user to the /files subpath from the main path