Implement Agent.proposals query

[fosterlynn]

For the textile lab app, we need to bring up all the open proposals for an agent, as part of getting other information for that agent. The proposals query isn't implemented yet.

Logic: For a specific agent (id), get all Proposals where the agent is a provider or receiver on any Intent related to that Proposal, and the Proposal.hasEnd is in the future. Or perhaps that last item is a filter?