[Echo.API.Request] update deferred object in case of abortion/close/error;
[Echo.StreamServer.API] update nextSince machinery; update requestType parameter in case of using skipInitialRequest;
[Echo.StreamServer.API.WebSockets] update nextSince from sunscribe/reset message if provided; implement logic to minimize view updates (maxResetsPerPeriod);
[Tests] add tests for the WS machinery; fix tests;
minor fixes.