Prepare 4 12x12 inch pieces of foil and set aside. Drizzle salmon with olive oil, rub over whole surface, then season with salt, pepper, and half of the Italian seasoning dried herbs. Repeat process with the shrimp. To make the sauce, stir together all ingredients in a bowl and set aside. Assemble foil packs by placing salmon in the middle, topped with 3-4 shrimp. Drizzle HALF of the sauce over the shrimp and salmon, RESERVE the other half for using later. Fold foil over the shrimp and salmon and pinch edges to seal closed so no juices leak. Grill foil packs over medium-high heat salmon-side down for 10 minutes, then flip and cook another 5 minutes or so until shrimp is opaque and salmon is cooked through and flaky. Drizzle with the reserved sauce (you may need to microwave it for a few seconds first if the butter has cooled) and top with additional fresh chopped dill if desired and serve.