#494 Add unique classes and id's for styling

[Steve Kenow]

I have worked to integrate this into Xoops, and there
are some pretty common class and id selectors used
throughout PGV - 'header', 'content', 'footer' are
most notable. Integration to other packages would be
much easier if you were to use classes and ids unique
to PGV: 'pgvheader', 'pgvcontent', and 'pgvfooter'