Debris interfacing

[jeffjennings]

Adds functionality for running fits with scale height inference from the terminal.

[rbooth200]

Looks good, happy to merge. My only comment is that it's valid to fit a debris disc with the log-normal model, we just don't have a way of evaluating whether the choice of h is good. I haven't tested it much though, so I don't know if the fitting with the log-normal method is working at all with the debris fitter

[jeffjennings]

Ok great, thank you. I've changed fit.py to not force method to Normal, just print a warning.