Conv no bias

• Add noBias for Conv & ConvDepthWise (and underlying MetaOperator)
• Add GraphView.logOuputs method to allow better debug

Minor modifications

• toString is now a virtual function of Data.

include/aidge/data/Data.hpp

@@ -52,7 +52,7 @@ public:
         return mType;
     }
     virtual ~Data() = default;
-    virtual std::string toString() const;
+    virtual std::string toString() const = 0;
 
 private:
     const std::string mType;