Add pagination in the get all operation

[jwalcorn]

Today if you do a GET /broker/, that returns all of the brokers that exist. That's fine if you only have a few, but if you had thousands or more, this isn't a good idea, as we could run the server out of memory, response time could be too long, etc. Need to add a way to ask for the first 20 or 100 or whatever, then ask for the next page in a separate REST call, etc. Of course, this means the downstream microservices, like Portfolio and Account, would similarly need such pagination. We'd probably also need to add some kind of "order by" support, to make sure we get the same first 100 from Portfolio that we get from Account.