DynamicLagrangeDiscreteFunctionSpace
This patch introduces a new alias for LagrangeDiscreteFunctionSpace to allow the choice of the polynomial order dyanmically. Most of this functionality was implemented already. The only LagrangeDiscreteFunctionSpace work exactly as before. Only, the static member variable polynomialOrder was renamed to maxPolynomialOrder. If this approach is acceptable I will also do this for the DG spaces.