Improves node.image program
Improves node.image program

Details:
- Crops images so that they'll be drawn in the nodes as if they had
background-size: cover and background-position: center in CSS
- Caps images max size to 100px in the textures (since this program uses
the gl.POINTS method and will never draw nodes bigger than 100px)
- Requires syncly a rendering when receiving a batch of images instead
of scheduling it, to prevent desyncs between the texture and the nodes
data

jacomyal/sigma.js,jacomyal/sigma.js,jacomyal/sigma.js