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_LB.hpp

@@ -160,7 +160,7 @@ public:
 
   /// method the get the number of vertices stored for the local domain
   /// @return number of local vertices
-  const int getNVertices() { return vertices.size(); }
+  int getNVertices() { return vertices.size(); }
 
   /// method to set undefined method specific data, which is not shared between
   /// different methods but needs to be set by a unified interface