Update csv when masterfiles updated

[Femkemilene]

This seeks to automatically update the csv files when the masterfiles is newer than the newest csv files. I think this will make it easier to update the model / switch between branches with different data. Should we try do finish this at the summer school?

Doesn't quite work yet, but nearly done:

• It seems to update all csv files when one masterfile is updated
• It's asking for confirmation to overwrite gamma values even when not

[Femkemilene]

@ldxib2: would you be able QA this one? If not, could you find somebody else to do it? @cormacmlynch: I know you wanted to ensure behaviour that gamma values aren't overwritten. Under the condition that the Masterfile is newer than the newest csv, the default behaviour is to overwrite. Is that okay? @pv-camecon: you said you would QA the model update in a week or 2. Without this PR, the model update requires you to manually run convert_masterfiles_to_csv.py. Otherwise, there will be an error. To avoid errors for others using the model, I think this PR needs to be tested & approved first.