Use file.name instead of file.url for getting name of file in GalleryImage

`file.name` is universal accross storages and can be used not only with
FileSystem storage but with S3 storage as well (`file.name` is used to
create the url). Also with using `name` instead of `url` we will not have
problems with encoding and python version.
Merge
Version bump to 3.0.8
Added tag 3.0.8 for changeset 42772f0ec915
Update auto generated CHANGELOG, requirements, settings docs.