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

function assertIsMember(v, allowed)
    assert(ismember(v, allowed), 'Expected ''%s'' to be in the set %s', inputname(1), toString(allowed));
end