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/utils/eoIntBounds.cpp

@@ -81,7 +81,7 @@ eoIntBounds* eoGeneralIntBounds::getBoundsFromString(std::string _value)
         }
 
       // now create the embedded eoIntBounds object
-      eoIntBounds * locBound;
+      eoIntBounds * locBound = nullptr;
       if (minBounded && maxBounded)
         {
           if (maxBound <= minBound)