AngelsPond adds cross-organization connection scopes

Connections between organizations in AngelsPond can now be scoped to individual systems. An organization granting a partner or supplier access chooses which systems that access reaches, instead of opening the connection as a whole.

Access granted wholesale is hard to reason about later: the organization that granted it has to remember what the connection implied. A per-system scope makes the grant explicit at the moment it is made, and legible afterwards.