Fix "make clean" rule. Moved class_grapher drush plugin to apps/.

Makefile

@@ -1,2 +1,2 @@
 clean:
-	find . -name "*.gv" -o -name "*.svg" -o -name php_errors.log -delete
+	find . \( -name "*.gv" -o -name "*.svg" -o -name "*.png" -o -name php_errors.log \) -exec rm {} \;