Make it possible to exit the printer demo

... by clicking on the power button :-)

Calling exit is a big rough, but simplest and fastest for now.

examples/printerdemo/cpp/main.cpp

@@ -9,7 +9,6 @@
 LICENSE END */
 #include "printerdemo.h"
 
-
 struct InkLevelModel : sixtyfps::Model<InkLevel>
 {
     int row_count() const override { return m_data.size(); }
@@ -25,5 +24,6 @@ int main()
 {
     static MainWindow printer_demo;
     printer_demo.set_ink_levels(std::make_shared<InkLevelModel>());
+    printer_demo.on_quit([]() { ::exit(0); });
     printer_demo.run();
 }

examples/printerdemo/rust/main.rs

@@ -28,5 +28,9 @@ pub fn main() {
         InkLevel { color: sixtyfps::Color::from_rgb_u8(0, 0, 0), level: 0.80 },
     ]));
 
+    main_window.as_ref().on_quit(move || {
+        std::process::exit(0);
+    });
+
     main_window.run();
 }

examples/printerdemo/ui/printerdemo.60

@@ -229,6 +229,7 @@ SettingsPage := Page {
 
 TopPanel := Rectangle {
    property<int> active_page: 0;
+   signal quit();
 
    color: white;
 
@@ -255,6 +256,14 @@ TopPanel := Rectangle {
         source: img!"images/power.png";
         width: root.width / 20;
         height: root.width / 20;
+
+        TouchArea {
+            width: parent.width;
+            height: parent.height;
+            clicked => {
+                root.quit();
+            }
+        }
     }
 }
 
@@ -264,6 +273,7 @@ export InkLevel := {
 }
 
 MainWindow := Window {
+    signal quit();
 
     width: 800lx;
     height: 600lx;
@@ -283,6 +293,7 @@ MainWindow := Window {
         active_page: root.active_page;
         width: root.width;
         height: root.width / 20 + 10lx;
+        quit => { root.quit(); }
     }
 
     for page_info[idx] in [