cubicweb-file #1507 have a medium size thumbnail available [open]

Right now in the code we can use "small" in the req and it produces a 75x75 pixels image. It would be nice to have a "medium" option to have a 350x350 thumbnail (for blogs for example).

prioritynormal
typeenhancement
done in<not specified>
load1.000
load left1.000
closed by<not specified>