Support Mass-delete with multiple pks

`contrib.sqla.view.ModelView.action_delete()` now is able to mass-delete models with multiple primary keys. Therefore, two new helper functions has been introduced in `contribg.sqla.tools`:

* `tuple_operator_in()` that fakes the `sqlalchemy.tuple_` operator for engines, that do not support the `tuple_` operator. (like sqlite)
* `get_query_for_ids()` that returns a query, object that contains all objects identified by the `ids`.

Both functions have docstrings with more information.

The logic of the `action_delete()` did not change, as for objects with a single primary key, the codepath did not change at all.