Add IANA registries

[mickenordin]

This PR adds IANA registires for:

• notifications
• resourceTypes
• shareTypes
• protocols
• share payloads

It also registers OCM-MLS notification entries.

The idea with the registries is to try to find where the extension points of OCM should be. We want the protocol to be extensible AND interoperable. Where the spec is unclear or under-developed interoperability suffers. If we add extension points to the specification with out making it possible to explain how to use that extension point, only proprietary single vendor extensions are possible.

So for example writing in the specification text, that other kinds of notifications are allowed and that implementors MUST ignore notifications they don't understand, is adding an extension point, that is guaranteed not to be interoperable. The registries make sure that we get both extensibility AND interoperabilities at the same time.

[glpatcern]

Thanks Micke, I have a couple of fixes and a conceptual question

[glpatcern]

Some more comments. I start to get the principle, that is we define a way for implementers to extend the spec in the parts that may be extended, without needing to touch the core spec. This is very good in view of a final RFC.

[glpatcern]

I think the current state is the best solution. It seems we need some IANA expert to decide whether what is here makes sense.

We haven't reached an agreement on how to populate the Registry of share payloads yet.