add NamedStringIO
add Gotoshop::Thumbnail
add HexdigestNamedVersion
add thumbnail version to ShopLogoUploader
add CreateLogoThumbnailWorker
generate logo thumbnail after save
use shop logo thumbnails
generate shop logo thumbnail iff logo changed
fix CreateLogoThumbnailWorker to work iff logo is present
Merge branch 'feature/generate-logo-thumbnails'