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 extends \BaseObject