Added WebPack2

This actually makes the JS bundler significantly bigger (170KB), but WebPack2 is the actively maintained
version and they are working on implementing further optimisations (see https://webpack.js.org/vote/ )

client/lib/calypso-boot/index.js

@@ -1,5 +1,5 @@
 import ReactClass from 'react/lib/ReactClass';
-import i18n from '../mixins/i18n';
+import { initialize, mixin } from '../mixins/i18n';
 
 export default function boot() {
 	// Initialize i18n
@@ -9,9 +9,9 @@ export default function boot() {
 		i18nLocaleStringsObject = window.i18nLocaleStrings;
 	}
 
-	i18n.initialize( i18nLocaleStringsObject );
+	initialize( i18nLocaleStringsObject );
 
-	ReactClass.injection.injectMixin( i18n.mixin );
+	ReactClass.injection.injectMixin( mixin );
 }
 
 boot();

client/lib/mixins/i18n/index.js

@@ -3,20 +3,14 @@
 // as implement our own translation logic, that could involved the server.
 let translations = {};
 
-const initialize = ( newTranslations ) => {
+export const initialize = ( newTranslations ) => {
 	translations = newTranslations;
 };
 
-const translate = ( text ) => {
+export const translate = ( text ) => {
 	return ( text in translations ) ? translations[ text ] : text;
 };
 
-const mixin = {
+export const mixin = {
 	translate,
 };
-
-export default {
-	initialize,
-	translate,
-	mixin,
-};

karma.conf.js

@@ -27,7 +27,7 @@ module.exports = function( config ) {
 				{ type: 'text-summary' },
 			]
 		},
-		webpack: Object.assign( baseWebpackConfig, {
+		webpack: Object.assign( baseWebpackConfig(), {
 			entry: {},
 			isparta: {
 				embedSource: true,