Clients' requests fairness

The RequestPool holds queues, one per each client id. Once it receives a request it calls the RequestInspector to extract the ClientID and adds the request to the respective client's queue. When batching requests to create a new Proposal the requests are chosen in a round-robin fashion from the queues. Queues are removed when empty.

An application which uses this library can choose how to delegate the different client ids. For example, if clients belong to different organizations, and the application wishes to have fairness between organizations' requests, rather than clients' requests, it can return the same ClientID from the RequestInspector for all clients belonging to the same organization.