Move model parameters to be an array

[aarmey]

We should be able to turn the current parameter structures into arrays with RecursiveArrayTools.jl and LabelledArrays.jl. This may require many code changes, but I'm hopeful with the two array packages that it wouldn't be too extensive. This would enable using ModelingToolkit to vastly speed up solving.

[aarmey]

A first step would just be to play around with this and see if you understand how the two packages work. If this ends up setup correctly the tests should pass.