[wip]Making swarm query node always return checkin

@hbeeken , as discussed with @knolleary today, the query nodes will always have to return something. Therefore I modified the Swarm query node to ensure that its behaviour is consistent with what I implemented in the Instagram node.

Started working on this too as @hbeeken is out of office until Wednesday. Also did some tidy-up whilst I was there.

I expect the unit tests to fail (although the node looks to be working OK) so hence the WIP tag until I get those working.
Using a variable in a closure or using a node property really achieves the same thing in this case. The distinction is that a property will be accessible in other node methods and to other users of the node object where as the variable in the closure will not.

@knolleary I've been thinking about whether we shouldn't just make a `red/node/Node.js' method like the [FitbitInNode.setInterval()](https://github.com/node-red/node-red-web-nodes/blob/master/fitbit/fitbit.js#L244) one so that we can have some consistency and more control (if for instance we want to configure short intervals for a demo). (Aside: I'm not sure why the interval !== null check that I just copied from elsewhere is meaningful.)