Download the images resulting from the API calls

[COrtsJosep]

Do this by storing the images in a sensible way, in a sensible structure of folders and sub-folders, with unique identifiers.

• [x] #18
• [x] #25
• [x] #28
• [ ] #20
• [x] #19
• [x] #21
• [ ] Actually execute the download.
• [x] #29