This method pass in revue all the non null terms (topological sens) and
run a functor on them. The functor is expected to have 3 arguments:
- 2 integer i and j that contains row and column index of term.
- one T val corresponding to term's value.
The functor can do anything you want.

This function offers to user a quick way to deal with all traits.
It may be slightly less efficient then calling getMemoryAcces and by
hand pass in in revue terms according to traits (to be checked). It
depends on what you do.

It will be used internally to replace many duplicated piece of code
where looping on all terms is required. It is already in use with
printMatrixMarket method. Has some test do check matrix market outputs
we can already conclude that forEach is validate.