Uses Aplpy FITSFigure in Npred plots

Still a few things to do here (I haven't figured out how to do these yet).
- [ ] Add colourbars to the plots
- [ ] Use better colour scale for the background ratio image
- [ ] Add titles to each of the subplots
Anything else?
This doesn't seem to work unless vmin=0 (I just get a uniform blue square if I use a different vmin value), which isn't great for getting a decent ratio image as all the values are close to 1. Do you know if this is a bug? Or am I just doing something wrong?