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

handlers/handlerpageview.cpp

@@ -26,7 +26,12 @@ SOFTWARE.
 
 bool HandlerPageView::canAccess(std::string page)
 {
-	return this->userSession->user.permissions.canRead();
+	return effectivePermissions(page).canRead();
+}
+
+std::string HandlerPageView::accessErrorMessage()
+{
+	return "You don't have permission to view this page";
 }
 
 std::string HandlerPageView::createIndexContent(IParser &parser, std::string content)