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/button.ts

@@ -50,7 +50,9 @@ function displayButton ({
   buttonContainer.append(button)
 }
 
+export type {
+  displayButtonOptions
+}
 export {
-  displayButtonOptions,
   displayButton
 }

client/videowatch/buttons.ts

@@ -103,6 +103,8 @@ export {
   closeSVG,
   openChatSVG,
   openBlankChatSVG,
-  shareChatUrlSVG,
+  shareChatUrlSVG
+}
+export type {
   SVGButton
 }

client/videowatch/uri.ts

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