Implement bake layer as image(s)

[ucupumar]

There's an option to bake a mask as an image, there also should be one for layer.

• [x] Bake layer as image on realtime layer (AO, edge detect, and fake lighting)
• [x] Make baked realtime layer to be reusable
• [ ] Bake layer that has multiple socket outputs
• [ ] Bake layer group