Laplace* operators

Why do we have separate laplace operators? Those should all be consolidated under the more general convectiondiffusion* implementations.

So all of the Laplace operators should be cleaned up and also deprecated (both the classes and the include files). If there are any examples in the howto, either port them over to convectiondiffusion or delete them if they are redundant because there is already a similar program using the convectiondiffusion operators.