Google App Engine - Java-backend and Angular-frontend in a single project

I am building a Angular 2 web app which uses a Java GAE / Cloud Endpoints API as backend. My aims are to

1. run both in a single Google Cloud Platform project my-project
2. edit both parts in a single project folder using e.g. IntelliJ IDEA, without having to switch between two IDEs/projects.

My status quo is as follows:

Currently, I have an Java App Engine project folder containing my API. This is currently deployed on my-project. I use IntelliJ IDEA to edit it. Basic structure of my backend project folder:

Backend
    .idea
    src/main
            java //My entire code is here
            webapp
                index.html //Just a stub
                WEB-INF
                        appengine-web.xml
                        web.xml
                        logging.properties
    build.gradle
    pom.xml
    <Some other files>

Furthermore, I have an Angular 2 project folder with my frontend seperately. Until now, I have only tested this web app locally and have never deployed it. I have used WebStorm to edit it. Basic folder structure:

Frontend
    e2e
    node_modules
    src
        app
        assets
        environments
        index.html
        stlyes.css
        <Some other files>
    angular.cli.json
    package.json
    <Some other files>

Now, how can I merge these two parts into one project to achieve what I have stated above?