Reorganization of requirements

Hi all,

It seems that the discussion on requirements is likely too long to fit on a
single Wiki page so I re-modelled the page [here](
http://www.w3.org/community/ontolex/wiki/Specification_of_Requirements), so
that each specific requirement has its own page.

I also propose we merge "Valence and Ontological Mapping" and "High-Order
Predicate Mapping", as I can't figure out how they differ

Regards,
John