Swap animal functional group config to CSV

[davidorme]

With #1060, the PlantsModel has dropped support for configuring individual PFTs via arrays of tables in TOML and moved solely to supporting configuration option pointing to a CSV file of PFT details. At the moment, the AnimalModel only supports that array of tables option, which is not a nice user experience.

We should move the AnimalModel over to a configured CSV path of functional group definitions.

This issue has been approved by @TaranRallings