Streamline lastgenre singleton log with album log

It was rather confusing that the lastgenre plugin, when handling
singletons, sometimes showed that it applied genres from last.fm and
sometimes didn't (it did only in debug log). This streamlines the
behaviour:

- Change debug to info log.
- Streamline wording.
- Display details about the track.

beetsplug/lastgenre/__init__.py

@@ -441,10 +441,10 @@ def lastgenre_func(lib, opts, args):
                 # an album
                 for item in lib.items(ui.decargs(args)):
                     item.genre, src = self._get_genre(item)
-                    self._log.debug(
-                        "added last.fm item genre ({0}): {1}", src, item.genre
-                    )
                     item.store()
+                    self._log.info(
+                        "genre for track {0} ({1}): {0.genre}", item, src
+                    )
 
         lastgenre_cmd.func = lastgenre_func
         return [lastgenre_cmd]