[Import Tool] Tool cannot be used to import an image to an extended hippogallery:imageset type

If the configuration property 'galleryFolderGalleryTypes' is used in the applicationContext.xml and it defines a gallery type that extends hippogallery:imageset, then the importing of images will most probably fail with an ItemNotFoundException.

The usage of the property 'galleryFolderGalleryTypes', and the applicationContext.xml in general is undocumented (only appears in the javadocs). See HIPPLUG-653

The problem with extending the hippogallery:imageset is Jackrabbit related. The cnd of it specifies:

[hippogallery:imageset] > hippo:document
orderable
......
+ hippogallery:thumbnail (hippogallery:image) = hippogallery:image primary mandatory autocreated
.....

When you extend this type, the specifiers 'primary' and 'autocreated' do _not work_. So, in the import tool,
org.onehippo.forge.migration.DocumentCreator#createImageBinary line 623 throws an ItemNotFoundException.