Fill chart series in python

QML doesn't have a method for replacing all points at once, which makes
it extremely slow when loading large profiles

ui/main_window.qml

@@ -29,13 +29,8 @@ ApplicationWindow {
         }
 
         function onProfileChanged(data) {
-            profileSeries.clear();
-            var last_x = 0;
-            for (var point of data) {
-                profileSeries.append(point[0], point[1]);
-                last_x = point[0];
-            }
-            axisX.max = last_x;
+            profile_handler.fill_series(profileSeries);
+            axisX.max = data[data.length - 1][0];
             axisX.applyNiceNumbers();
         }
     }