Implemented KotoIndexedArtist as well as KotoIndexedAlbum, including moving the file indexing capabilities into the KotoIndexedAlbum (subject to change).
Added g_debug messages instead of using g_message for debug purposes. Re-introduced Koto Utils with new koto_utils_get_filename_without_extension, since that is used to get the extensionless file name across both album fetching and base file name fetching.
