merge: issue/0031 — animation curves (timeline + bezier_editor + tween_curves)

# Conflicts:
#	cpp/apps/primitives_gallery/CMakeLists.txt

cpp/apps/primitives_gallery/demos.h

@@ -21,6 +21,9 @@ void demo_dashboard_panel();
 void demo_text_editor();      // wave 1, issue 0025
 void demo_file_watcher();     // wave 1, issue 0025
 void demo_process_runner();
+void demo_tween();            // issue 0031
+void demo_bezier_editor();    // issue 0031
+void demo_timeline();         // issue 0031
 
 // --- Viz ---
 void demo_bar_chart();