improve RTL workflow

src/app.h

@@ -88,6 +88,7 @@ public:
     bool redraw = true;
     bool animate = false;
     bool ui_visible = true;
+    bool ui_rtl = false;
     bool vr_active = false;
     glm::mat4 vr_controller;
     glm::vec3 vr_controller_pos;
@@ -210,6 +211,8 @@ public:
 
     void ui_save();
     void ui_restore();
+    void set_ui_rtl(bool rtl);
+    bool get_ui_rtl() const;
 
     void cmd_convert(std::string pano_path, std::string out_path);
 };