refactor: Change Node::initError to take bilingual_str

Make it consistent with `Chain::initError`.

src/interfaces/node.h

@@ -45,7 +45,7 @@ public:
     virtual ~Node() {}
 
     //! Send init error.
-    virtual void initError(const std::string& message) = 0;
+    virtual void initError(const bilingual_str& message) = 0;
 
     //! Set command line arguments.
     virtual bool parseParameters(int argc, const char* const argv[], std::string& error) = 0;