Terminology: use role names, not entity names where appropriate

[jernst]

The protocol can be used in different organizational constellations, in particular:

• There may or may not be an Authorized Agent: the User may perform all the responsibilities of an Authorized Agent themselves
• There may or may not be a Privacy Infrastructure Provider: the Covered Business may perform all the responsibilities of a Privacy Infrastructure Provider themselves

Given this, some of the terms should be adjusted to apply in all of those cases, specifically:

• the Authorized Agent Interface is really an interface to software run by whoever performs the role that the Authorized Agent plays (if it exists for a given User) or that the User plays themselves. Maybe Data Rights User-side Interface or something like that.
• the PIP Interface is really an interface to software run either by a PIP or the CB themselves. Maybe Data Rights Business-side interface or something like that.

Also, in the terminology section, it may be useful to indicate that some of these roles are optional, and a couple diagrams showing those different constellations would do wonders for comprehensibility IMHO.