Fix support of baseClass attribute for table with namespaces.

Fixes issue #209. Format is simply dotted notation, eg.

    <database name="simple_database">
        <table name="inheriting_table" baseClass='Foo.Bar.Baz'>
            <column name="id" required="true" primaryKey="true" autoIncrement="true" type="INTEGER" />
        </table>
    </database>

Note that the table inherited must extend \BaseObject