Add functions, roles, and object models to draft

This updates IETF-RFC.md with a significantly expanded conceptual
framework for OCM. It introduces formal definitions of OCM functions,
clarifies the roles of Sending and Receiving Servers, and adds detailed
object models for Address Books, Contacts, Invites, Providers, Shares,
Users, and Resources. The change reorganizes and expands terminology,
adds diagrams to illustrate relationships, and alphabetizes and
harmonizes defined terms. Legacy duplicated sections are removed or
merged into the new structure.

Signed-off-by: Micke Nordin <[email protected]>

Author: mickenordin