Instagram node

This is my attempt on the Instagram node. Current example is showing the query node. Comments are welcome. I'll squash commits once we get this work into a pullable state. Thanks

The pull request is now ready @knolleary .
If you had multiple input nodes, each would set their own polling interval, but the global `interval` would get overwritten to point at the last one to initialise. `interval` should be `node.interval`, and then the node's on-close function should reference that way.