Logged: add a note to generalize in the future

When a type is Logged, it has a Logger, not necessarily a LogService.
But for now, for backwards compatibility, we cannot change it yet.

Author: ctrueden

src/main/java/org/scijava/log/Logged.java

@@ -40,5 +40,6 @@
 public interface Logged {
 
 	/** Gets the {@link LogService} to use when logging activities. */
+	// TODO: SJC3: Generalize to Logger instead of LogService.
 	LogService log();
 }