Although expressions have args and function as a tree, args cannot be
modified. So tree-transformations are not possible.
Sympy has subs function, however it replaces all matched in any
subexpression, of the expression (i.e. not only in args but in args args
and so on).

Move my llvm demo notebook in the correct folder

- colored dot output of AST
- various display helpers used in documentation

and not as a string.
Changed name of the file TypedSymbol to types.
Fixed usage of dtype accordingly, however i might not have found every
usage of dtype.

- new waLBerla only benchmark

- wrote a new, separate lattice model for cumulants
- tested with 2D LDC

problem in moveConstantBeforeLoops transformation:

--> a should end up here
{
for() {
  const int a = 5;
}
for() {
  const int a = 5
}
}

the "a" of the lower loop was not moved up, since it could not move across first loop (which is wrong)