[enh] flickr_noapi: use complete JSON data block, add 'content', 'img_format', 'source', etc. (#1571)

Fetch complete JSON data block, use legend to extract images. 
Unquote urlencoded strings.
Add image description as 'content'. 
Add 'img_format' and 'source' data (needs PR #1567 to enable this data to be displayed). 
Show images which lack ownerid instead of discarding them.