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/tsconfig.json

@@ -13,6 +13,9 @@
 		"noImplicitReturns": true,
 		"strictBindCallApply": true, // should already be true because of strict:true
 		"noUnusedLocals": true,
+		"allowSyntheticDefaultImports": true, // Seems necessary for peertube types to work
+		"isolatedModules": true, // Needed by esbuild https://esbuild.github.io/content-types/#isolated-modules
+		"esModuleInterop": true, // Needed by esbuild https://esbuild.github.io/content-types/#es-module-interop
     "outDir": "../dist/client",
 		"paths": {
 			"shared/*": ["../shared/*"]