split app.cpp into multiple files, add NodeScroll and use it to scroll the side panels, some fixes to the events system

engine/node_canvas.cpp

@@ -162,12 +162,12 @@ kEventResult NodeCanvas::handle_event(Event* e)
 
     switch (e->m_type)
     {
+    case kEventType::MouseScroll:
     case kEventType::MouseDownL:
     case kEventType::MouseUpL:
     case kEventType::MouseDownR:
     case kEventType::MouseUpR:
     case kEventType::MouseMove:
-    case kEventType::MouseScroll:
     case kEventType::MouseCancel:
         for (auto& mode : *m_canvas->m_mode)
             mode->on_MouseEvent(me, loc);