Allow better filtering on the `payments` endpoint

[MariusVanDerWijden]

Abstract

Querying the payments endpoint returns all previous payments. If you're building an app that does a lot of payments, these add up pretty quickly. It would be great if you could add filter arguments to your query to limit the amount of data between the raiden node and your app.

Specification

In the readthedocs it says that you can provide a limit and an offset to the payments endpoint. Unfortunately there is currently no reference for this which should be added to make it more useful. Additionally it would be great to filter for specific arguments to limit the amount of data between the raiden node and your app. Things like log_time </==/> specified_time Event ==/!= EventPaymentSentSuccess or query by token or target.

Add an optional parameter query= or something similar to the payments endpoint

Backwards Compatibility

No issues, queries without the optional parameter will just return the current behaviour