userDao: Implement list()

database/userdao.h

@@ -3,6 +3,7 @@
 #include <string>
 #include <optional>
 #include "../user.h"
+#include "queryoption.h"
 class UserDao
 {
   public:
@@ -10,6 +11,7 @@ class UserDao
 	virtual bool exists(std::string username) = 0;
 	virtual std::optional<User> find(std::string username) = 0;
 	virtual std::optional<User> find(int id) = 0;
+	virtual std::vector<User> list(QueryOption o) = 0;
 	virtual void deleteUser(std::string username) = 0;
 	virtual void save(const User &u) = 0;
 	virtual ~UserDao(){};