Feat: Adds js alias to root/app/js

Issue #77

Found the best explanation here:
https://webpack.js.org/configuration/resolve/#resolvealias

With this setting, all files and folders in js can now
be referenced with the js alias,
e.g. a module app/js/module.js should be imported in
index.js as js/module.js.

app/js/foo/hello.js should be imported in index.js as
js/foo/hello.js.

inst/templates/node/webpack.config.babel.js

@@ -3,6 +3,11 @@ import { join } from 'path';
 export default {
   mode: 'production',
   entry: join(__dirname, 'root', 'app', 'js', 'index.js'),
+  resolve: {
+    alias: {
+      js: resolve(__dirname, 'root/app/js'),
+    },
+  },
   output: {
     library: 'App',
     path: join(__dirname, 'root', 'app', 'static', 'js'),