Rearrange images

[Pratichhya]

I notice that a lot of these new images are in the root of the _images folder and have very short generic names like "save.png", "bbox.png", "bands.png", while they are specific to the webeditor. I think it is more future-proof to give a more specific name, or put them in a subfolder.

As suggested in #233 images needs to be rearranged to a specific folder for better management and renamed if needed.