Produce and use webp pictures with different sizes

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/utils/support.ts

@@ -0,0 +1,10 @@
+export function supportsWebPFormat(): boolean {
+  const elem = document.createElement("canvas");
+
+  if (elem.getContext && elem.getContext("2d")) {
+    // was able or not to get WebP representation
+    return elem.toDataURL("image/webp").indexOf("data:image/webp") === 0;
+  }
+  // very old browser like IE 8, canvas not supported
+  return false;
+}