Modularity of the Floe Struct

[skygering]

I think it would be nice if the Floe fields were organized into different sub-structs whose type influences the type of the Floe.

For example, all of the information needed for time stepping could be in a TimeSteppingInformation struct that is a concrete type AbstractTimeSteppingInformation. Then it would be really easy to try different time stepping methods without having to completely re-write the code base.

This might also just make it easier to read and understand given the Floe struct is massive.

[skygering]

We will need a better idea of how this effects StructArrays: JuliaArrays/StructArrays.jl#85. This is a good start to understanding.