Export module for a website gallery with selected images

This export module should replace the PhotoSwipe copy in darktable.

See https://github.com/darktable-org/darktable/issues/16205 for more
details.

data/website_gallery/fullscreen.js

@@ -0,0 +1,40 @@
+var isFullscreen = false;
+
+var toggleFullscreen = function (ele) {
+    return isFullscreen ? exitFullscreen(ele) : requestFullscreen(ele);
+};
+
+var requestFullscreen = function (ele) {
+    if(isFullscreen == true) return 0 ;
+    
+    isFullscreen = true;
+    if (ele.requestFullscreen) {
+	ele.requestFullscreen();
+    } else if (ele.webkitRequestFullscreen) {
+	ele.webkitRequestFullscreen();
+    } else if (ele.mozRequestFullScreen) {
+	ele.mozRequestFullScreen();
+    } else if (ele.msRequestFullscreen) {
+	ele.msRequestFullscreen();
+    } else {
+	console.log('Fullscreen API is not supported.');
+    }
+};
+
+var exitFullscreen = function () {
+    if(isFullscreen == false) return 0;
+    
+    isFullscreen = false;
+    if (document.exitFullscreen) {
+	document.exitFullscreen();
+    } else if (document.webkitExitFullscreen) {
+	document.webkitExitFullscreen();
+    } else if (document.mozCancelFullScreen) {
+	document.mozCancelFullScreen();
+    } else if (document.msExitFullscreen) {
+	document.msExitFullscreen();
+    } else {
+	console.log('Fullscreen API is not supported.');
+    }
+};
+