Add an Empty grid class The need turned up for the flexural code when we may or may not have a grid for the open water and want to plot that solution. In case there is no open water we need an empty grid to plot the empty gridfunction against to avoid errors.

classdef Structured < grid.Grid
    methods (Abstract)
        % Returns the size of the grid in each dimension m = [mx my mz ...]
        m = size(obj); % Is this a good idea? Isn't immersed a structured grid?
        h = scaling(obj);
    end
end