Add a terminology section

[timcappalli]

This is a complicated ecosystem. We need a dedicated terminology section at the beginning of the spec (probably between scope and model).

We have a bunch of definitions scattered throughout different sections. We're also missing definitions for things like credential manager (holder is technically a person, not where the credential is stored, and that is an important entity).

Let's use this issue to aggregate terms which should be defined (the definition can be a reference to another spec).

Some to start:

• Issuer
• Verifier
• Holder
• Credential manager
• Wallet
• Client platform

[TallTed]

When the time comes to add this to the body of the document... A Glossary appendix can work well, or a Glossary section near the start. If presented with a lot of prose, it can be sensible to "build" the vocabulary, starting from a "keystone" term and building definitions as you add terms. This does not make sense in all cases. If presented as a bullet list or a table, I strongly advise putting the terms in alphanumeric order (using US English context, as needed), rather than any conceptual sort order, as readers usually have a fair idea of where to look in an alphanumeric ordering, but almost always have difficulty in figuring out the conceptual order used by any given author.

[marcoscaceres]

The following terms are defined in VC already, and we reference them as such:

• Issuer
• Verifier
• Holder

The "credential manager" would be Cred Man. Or we need a different concept.

That leaves:

• Wallet
• Client platform