Backport to 7.8 - Support gallery type selection when uploading new image through Xinha

When inserting an image into a Xinha richtext field, you may directly upload an image into the gallery. I'm attaching a diff that enables users to select the target image set for such an upload, based on the gallery folder's hippostd:gallerytype options. The diff is against the 2.22.xx branch, POM version is 2.22.16-SNAPSHOT.