GH-1556 disable export for tracked FTB instances

logic/minecraft/ftb/LegacyFTBInstance.h

@@ -10,4 +10,8 @@ public:
 	virtual QString id() const;
 	virtual void copy(const QDir &newDir);
 	virtual QString typeName() const;
+	bool canExport() const override
+	{
+		return false;
+	}
 };

logic/minecraft/ftb/OneSixFTBInstance.h

@@ -21,7 +21,10 @@ public:
 	QDir versionsPath() const override;
 	bool providesVersionFile() const override;
 	virtual QString typeName() const override;
-
+	bool canExport() const override
+	{
+		return false;
+	}
 private:
 	SettingsObjectPtr m_globalSettings;
 };

logic/minecraft/legacy/LegacyInstance.h

@@ -124,6 +124,11 @@ public:
 
 	virtual QString typeName() const override;
 
+	bool canExport() const override
+	{
+		return true;
+	}
+
 protected:
 	mutable std::shared_ptr<ModList> jar_mod_list;
 	mutable std::shared_ptr<ModList> core_mod_list;

logic/minecraft/onesix/OneSixInstance.h

@@ -94,6 +94,11 @@ public:
 
 	virtual QString typeName() const override;
 
+	bool canExport() const override
+	{
+		return true;
+	}
+
 signals:
 	void versionReloaded();