Feature/fix warnings

We should be able to compile using -Wall -Wextra -Werror.

Currently the easy fixes are done, but in the Unstructured load balancer many variables are declared (and set), but not used. I assume, this is the case due to the in progress state of the method.

Other open problems are:

• unused parameters for some implementations of setAdditionalData. If these declaration have to be there we may silence them with proper annotations (for GCC: __attribute__((unused))(ref), which should be put into a compiler dependant preprocessor switch to also set this for clang etc. as well as for readability. Maybe known_unused is a good keyword)
• ignored const on function return (ALL_LB.hpp:163: const int getNVertices() { return vertices.size(); })

This branch should only be merged to refactor after !9 (merged) has been merged!.

include/ALL_Staggered.hpp

@@ -344,7 +344,6 @@ template <class T, class W> void Staggered_LB<T, W>::balance(int) {
 }
 
 template <class T, class W> void Staggered_LB<T, W>::find_neighbors() {
-  int dimension = this->getDimension();
   auto work = this->getWork();
   auto vertices = this->prevVertices;
   auto shifted_vertices = this->vertices;