Use ESBuild for frontend build.

Replacing webpack by ESBuild for client code compilation (as in the
official quickstart plugin).

So we can remove deprecated webpack dependencies.

Note: webpack is still used for ConverseJS build.
This may be removed soon.

Related to issue #122.

client/videowatch/uri.ts

@@ -66,8 +66,10 @@ function getIframeUri (
   return iframeUriStr
 }
 
+export type {
+  UriOptions
+}
 export {
-  UriOptions,
   getBaseRoute,
   getIframeUri
 }