Remove annoying getters & setters

[nmheim]

The getters and setters we currently use in the Ecosystem are only there because of the ⚥Sheep type which should demonstrate the forwarding of fields. We could get rid of all of them by overloading getproperty (and setproperty!) for ⚥Sheep instead:

function Base.getproperty(s::⚥Sheep, x::Symbol)
    if x == :sex || x == :sheep
        getfield(s,x)
    else
        getfield(s.sheep,x)
    end
end

[nmheim]

closed in favour of #61