disable brush pressure averaging, implement single finger for camera rotation when touch draw is disabled

src/app_events.cpp

@@ -303,3 +303,10 @@ void App::toggle_ui()
         m->m_children[i]->m_display = fullscreen;
     fullscreen = !fullscreen;
 }
+
+void App::set_stylus()
+{
+    has_stylus = true;
+    if (canvas)
+        canvas->m_canvas->m_touch_lock = true;
+}