Add support to "operation tagging" to ListSubHandler and DictSubHandler.

Add support to "operation tagging" to ListSubHandler and DictSubHandler.

"Operation tagging" means that if the contained objects has an _add,
_update or _delete attribute, it set them to true when the item is
added, updated or deleted respectively (in case that it's deleted, it's
not removed from the container, but it's not listed either, i.e. the
items are "logically" deleted, not really removed from the container).

Now ListSubHandler and DictSubHandler ihnerit from a new class
ContainerSubHandler which handles 95% of the code. Because of this, now
the "magic" attributes starts with _cont_ instead of _list_ or _dict_.
Existing handler were updated, but new ones should take this into
account.