handlers: permisison check for all pages + retrieve user-specific permissions for pages (if any)

handlers/handlerallcategories.h

@@ -8,7 +8,9 @@ class HandlerAllCategories : public Handler
   public:
 	HandlerAllCategories();
 	using Handler::Handler;
-	Response handle(const Request &r) override;
+	Response handleRequest(const Request &r) override;
+	std::string accessErrorMessage() override;
+	bool canAccess(const Permissions &perms) override;
 };
 
 #endif // HANDLERALLCATEGORIES_H