Use webpack CLI instead of gulpfile.js

webpack.config.renderer.js

@@ -0,0 +1,28 @@
+module.exports = {
+  entry: {
+    index: './src/browser/index.jsx',
+    settings: './src/browser/settings.jsx',
+    'webview/mattermost': './src/browser/webview/mattermost.js'
+  },
+  output: {
+    path: './dist/browser',
+    filename: '[name].js'
+  },
+  module: {
+    loaders: [{
+      test: /\.json$/,
+      loader: 'json'
+    }, {
+      test: /\.jsx$/,
+      loader: 'babel',
+      query: {
+        presets: ['react']
+      }
+    }]
+  },
+  node: {
+    __filename: false,
+    __dirname: false
+  },
+  target: 'electron-renderer'
+};