Add basic implementation of deleteAll().
Add method to execute an ORM\Query and get a statement back.

It is sometimes useful to have access to the statement object. In the
case of updateAll/deleteAll, the row count is useful. Shoehorning the
rowcount into ORM\ResultSet felt more awkward.
Merge pull request #1369 from markstory/3.0-table-delete

3.0 - Add basic implementation of deleteAll().