Refactor of #73

PR overview of main changes:

• adds Parameters module with compute_darwin_parameters function, which generates n volumes for each plankton group and computes "emergent" parameters from those
  • makes use of NamedArrays
  • the emergent functions are just placeholders, this is also why they are kept in examples for now (to be moved to main library once implemented)
• adds a test that checks that emergent_parameters have the same values as those that were hand-coded in the N2P2ZD example

Small edits:

• rename the Dynamic module to Biogeochemistry, this means that models are now accessible as Agate.Models.Biogeochemistry.<struct UUID>
• update the NPZD example to avoid duplication of parameters (lᵖⁿ and lᶻⁿ were specified twice)