Add ObservableChangeManager interface with wrapper implementation

core/src/main/java/dev/kske/undoredo/core/ChangeManager.java

@@ -26,7 +26,7 @@ public interface ChangeManager<C extends Change> {
 	 * @return the change that was applied last
 	 * @since 0.0.1
 	 */
-	Optional<Change> getLastChange();
+	Optional<C> getLastChange();
 
 	/**
 	 * Undoes the current change.

core/src/main/java/dev/kske/undoredo/core/UnlimitedChangeManager.java

@@ -23,7 +23,7 @@ public final class UnlimitedChangeManager<C extends Change> implements ChangeMan
 	}
 
 	@Override
-	public Optional<Change> getLastChange() {
+	public Optional<C> getLastChange() {
 		return index == -1 ? Optional.empty() : Optional.of(changes.get(index));
 	}