[Feature] ImageController

[Jeremboo]

I recently needed to hack the lib to add a feature to test different images quickly.

I thought about something like that:

var images = { path1: 'myImage.png'};
gui.addImage(images, 'path1').onChange((image) => {
  console.log('do something with the image loaded');
});

Because I'll need it multiple time (and some people were interested too) I did a short library where you can see the usage: dat.gui.image.

I tested the code and the augmented functions (.name(), .listen(), .remove()).

Feel free to recommend me some updates in term of code or UX!

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[Jeremboo]

@googlebot I signed it!

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[andrevenancio]

When can we expect this to be merged?