fix stroke preview, add license messages, fix node scroll

src/app.cpp

@@ -371,6 +371,11 @@ void App::init()
     initAssets();
     initLayout();
     title_update();
+
+    if (!check_license())
+    {
+        message_box("License", "Could not validate this license, running in demo mode.");
+    }
     
     //GLfloat width_range[2];
     //glGetFloatv(GL_SMOOTH_LINE_WIDTH_RANGE, width_range);