Add server.js with basic express template

Add server.js with basic express template. We have created a very
basic example of a server which serves web pages built with Express.
We have changed this line:
```app.use(express.bodyParser())```
with these 2 lines, so we get rid of the error of Connect 3.0 [Source of the solution](https://stackoverflow.com/questions/19581146/how-to-get-rid-of-connect-3-0-deprecation-alert)
```
app.use(express.json());
app.use(express.urlencoded());
```

Contact: joaquin@isla.io