making signal and slots use appropriate signals

This makes it so other DataChanged signals don't reset the view as was
happening before.

src/qml/presenter/PreviewSlideListDelegate.qml

@@ -72,7 +72,7 @@ Item {
 
     Connections {
         target: SlideMod
-        function onDataChanged() {
+        function onActiveChanged() {
             if (active) {
                 previewSlidesList.currentIndex = index;
                 previewSlidesList.positionViewAtIndex(index, ListView.Center);

src/rust/slide_model.rs

@@ -655,7 +655,9 @@ mod slide_model {
             if let Some(slide) = self.as_mut().slides_mut().get_mut(index as usize) {
                 slide.active = true;
                 self.as_mut().emit_data_changed(tl, br, &vector_roles);
-                // self.as_mut().emit_active_changed(); // This function doesn't work
+                // We use this signal generated by our signals enum to tell QML that
+                // the active slide has changed which is used to reposition views.
+                self.as_mut().emit_active_changed();
                 println!("slide is activating {:?}", index);
                 true
             } else {