Rationalise location of functions which manage "types" of data.

[triangle-man]

Specifically, much of the functionality in utils/data.py might better live in the DataDescription class.

[JamesJordon]

As discussed, our general rule for going forward should be: if the functionality of a function is specific to a class, it should be a method on the class, but if it is more general it should live in utils. If unsure, I would suggest it gets placed in utils, to reduce the chance of it being overlooked when trying to identify whether or not we already have some piece of functionality.