Added nGraph as a public dependency (#6071)

* Added nGraph as a public dependency

* Fixed Windows warning

* Fixed CMake

* Fixed constant op

* Fixed typo

* Fixed comments

* Revert ngraph libraries

* Fixed build

* Fixed IE::ngraph

* Fixed git merge

inference-engine/samples/hello_reshape_ssd/reshape_ssd_extension.hpp

@@ -109,7 +109,7 @@ public:
         return std::make_shared<CustomReluOp>(new_args.at(0));
     }
 
-    bool visit_attributes(ngraph::AttributeVisitor& visitor) override {
+    bool visit_attributes(ngraph::AttributeVisitor&) override {
         return true;
     }
 };