Make file path parameters generic for each type of data

[thomaszwagerman]

Currently individual datasets have individual constructor parameters, for example:

# Temperature data options
frank_temps_file::String = "Data/FranksTemps.mat"
bisicles_temps_file::String = "Data/antarctica-bisicles-xyzT-8km.nc"

Even when they are the same "type" of data (Temperature, in this case).

Works for now, but ideally this is simpler, and a "type" of input data is controlled by a single parameter. This could get out of hand when there are many different possible data sources for a data category.

[thomaszwagerman]

The other flaw in the current implementation is that whether Franks or Bisicles is used is controlled by an if/else statement that checks for either parameter being provided. Not foolproof (e.g. when both are given it will prioritise Franks)