Update blueimp Gallery template.

index.html

@@ -200,14 +200,39 @@
     <div
       id="blueimp-gallery"
       class="blueimp-gallery blueimp-gallery-controls"
+      aria-label="image gallery"
+      aria-modal="true"
+      role="dialog"
       data-filter=":even"
     >
-      <div class="slides"></div>
+      <div class="slides" aria-live="polite"></div>
       <h3 class="title"></h3>
-      <a class="prev">‹</a>
-      <a class="next">›</a>
-      <a class="close">×</a>
-      <a class="play-pause"></a>
+      <a
+        class="prev"
+        aria-controls="blueimp-gallery"
+        aria-label="previous slide"
+        aria-keyshortcuts="ArrowLeft"
+      ></a>
+      <a
+        class="next"
+        aria-controls="blueimp-gallery"
+        aria-label="next slide"
+        aria-keyshortcuts="ArrowRight"
+      ></a>
+      <a
+        class="close"
+        aria-controls="blueimp-gallery"
+        aria-label="close"
+        aria-keyshortcuts="Escape"
+      ></a>
+      <a
+        class="play-pause"
+        aria-controls="blueimp-gallery"
+        aria-label="play slideshow"
+        aria-keyshortcuts="Space"
+        aria-pressed="false"
+        role="button"
+      ></a>
       <ol class="indicator"></ol>
     </div>
     <!-- The template to display files available for upload -->