Instagram test and Instagram node fixes

This is my work on adding the Instagram tests. A few issues might need to be sorted. I'll make comments in-line detailing these.
The comment doesn't make sense because ```DUMMY``` isn't -1 any more. I meant you to just search/replace ```DUMMY``` with ```null``` not set ```DUMMY``` to ```null```. But you probably don't need to give the node properties a default value at all. You can just do:

    !node.latestLikedID

rather than:

    node.latestLikedID === DUMMY