tidy the CIM (to make it less XML specific)

This page provides documentation for ticket:236.

(note: while I'm working I'll tag action items in bold)

changes to think about:

  1. From Phil's email:

On a related note, several of the attributes in the grid classes are optional (presumably this applies to the other packages too). However, I'm wondering if we shouldn't make all properties mandatory and instead handle empty/non-required values using standard null value mechanisms, e.g. empty tags in XML, NULL value in rdbms. I feel that this might make the CIM data model more easily transferable to different physical implementations.