Allow user to extend classes object via initialisation options

This will allow you to do things like:

    $('#my-table').dataTable({
        'oClasses': {
            'sWrapper': 'awesome-sauce'
        }
    });

I feel like it makes sense to have this ability since you can already do:

    $('#my-table').dataTable({
        'oLanguage': {
            'oPaginate': {
                'sPrevious': 'Retreat!',
                'sNext': 'Forward March!'
            }
        }
    });

... not that you would.