Events on threejs scene + edit from config.pixel folders

Hi @anvaka,

I'm using ngraph.pixel (after vivagraphjs) to render some RDF graphs, and I'm really impressed by what you've done !
It works great for my current needs, but I would suggest some new events / ways to edit a graph.
So many questions about differents modules, but I hope I'm in the right place.
### Events
- I know [context menus](http://caniuse.com/#feat=menu) are currently only supported by Firefox, but it would be a great improvement if we can catch a 'right click' event and be able to show some inputs.
- I didn't found how to catch a 'click' event from the scene.
On your [config example](https://anvaka.github.io/ngraph.pixel/demo/config/index.html?graph=balancedBinTree), we can click on a node, but if I click on the threejs scene just after, I wish it could clear the 'Current Node's folder.
- Do you think it's possible to add an area selection like the [vivagraphjs](http://anvaka.github.io/VivaGraphJS/demos/other/webgl-area-select) 'one, even if it's with the 2D layout ?
### Config.pixel

I've added many folders into the config.pixel to see some node's metadata from a SPARQL query.
- I didn't found how to add a submit button. It would be great to edit the text inputs and fire a callback.
- Again, I didn't found how to add a input into a folder.
### RDF

I saw somewhere that if we want to catch your attention, we may propose you to do something like impossible or nearly impossible to do.
You may know that a RDF graph isn't really a 'graph' but like a 'property graph' with many properties/links between 2 entities/nodes.
What do you think of a ngraph module to do something like that ?

Cheers,
Bruno

The issue points to the config example and three.js scene, but names no source file or test. Review the linked config.pixel demo and existing scene interaction modules first; the requested click, selection, form controls, and RDF support are separate proposals without a single completion criterion.

Written by the indexing model from the issue text.