fix new warnings and escape apply namespace

- `std::apply` is part of C++17 and the compiler wants to use it because
of ADL. Thus it is now necessary to escape it as `::apply`.
- remove some `using namespace std` remaining in the sources.
- fix simple warnings.

eo/src/eoTopology.h

@@ -80,7 +80,7 @@ public:
     /**
      * Prints the neighborhoods contained in the topology.
      */
-    virtual void printOn() = 0;
+    // virtual void printOn() = 0; // Already defined in eoPop
 };