Implement missing functions, fixes linking errors

lib/constants/IdentifierBase.h

@@ -0,0 +1,64 @@
+/*
+ * IdentifierBase.h, part of VCMI engine
+ *
+ * Authors: listed in file AUTHORS in main folder
+ *
+ * License: GNU General Public License v2.0 or later
+ * Full text of license available in license.txt file, in main folder
+ *
+ */
+#pragma once
+
+class IdentifierBase
+{
+protected:
+	constexpr IdentifierBase():
+		num(-1)
+	{}
+
+	explicit constexpr IdentifierBase(int32_t value):
+		num(value)
+	{}
+
+	~IdentifierBase() = default;
+public:
+	int32_t num;
+
+	constexpr int32_t getNum() const
+	{
+		return num;
+	}
+
+	constexpr void setNum(int32_t value)
+	{
+		num = value;
+	}
+
+	struct hash
+	{
+		size_t operator()(const IdentifierBase & id) const
+		{
+			return std::hash<int>()(id.num);
+		}
+	};
+
+	template <typename Handler> void serialize(Handler &h, const int version)
+	{
+		h & num;
+	}
+
+	constexpr void advance(int change)
+	{
+		num += change;
+	}
+
+	constexpr operator int32_t () const
+	{
+		return num;
+	}
+
+	friend std::ostream& operator<<(std::ostream& os, const IdentifierBase& dt)
+	{
+		return os << dt.num;
+	}
+};