Suggest: change datatype variable name in ML code

[Neves-P]

DAISIE_ML_CS contains the argument datatype, which can be single or multiple.

I suggest changing this name, as it implies (at least it lead me in that direction) that an ML run in a 2 species type scenario should be expected (i.e. run DAISIE_ML2). In fact, it determines if single island or archipelago scenario should be expected (and DAISIE_ML1 runs).

[richelbilderbeek]

I think it should be encouraged to make code more expressive. I am happy to read what the current name implies, but I wonder:

• What does the variable do?
• What do you suggest to name the variable to?

As a side-note, apparently you can also suggest better names for DAISIE_ML1 and DAISIE_ML2 as well 🌈