Code modernization: src/m* (part 3)

* empty function
* default constructor/destructor
* for range-based loops
* use emplace_back instead of push_back
* remove some unused headers in some cpp variable

src/mapnode.h

@@ -300,5 +300,5 @@ struct MapNode
 
 private:
 	// Deprecated serialization methods
-	void deSerialize_pre22(u8 *source, u8 version);
+	void deSerialize_pre22(const u8 *source, u8 version);
 };