Add general Runge-Kutta class - Add a general Runge-Kutta class which time integrates the solution based on coefficients obtained from a Butcher tableau - Add butcher tableau which returns coefficents for the specified Runge-Kutta method - Remove RungKutta4proper, since obsolete

% Converts a gridfunction to a plot matrix
% Takes a grid function and and a structured grid.
function F = funcToPlotMatrix(g, gf)
    F = reshapeToPlotMatrix(gf, g.size());
end