Create a tutorial on developing an app with Tabris.js

### Problem description

Currently the documentation does not provide an integrated guide on the development process with Tabris.js.

### Expected behavior

In order to give a richer impression about the development experience with Tabris.js, provide a guide about developing a full-fledged app (e.g. chat, TODO app...). The guide should be an extension of the _Quick Start Guide_. The _Quick Start Guide_ should link to it in its _Create your first app_ section.

In its essence, the guide should show how an idea is mapped to a working app using Tabris.js. Each tutorial step could be split into:

1. Defining a goal
2. Using the documentation* to find an API which contributes to reaching the goal
3. Integrating the API in the app code
4. Reloading the app to test the result

(*) *not necessarily using tabrisjs.com, maybe also demonstrate how to use VSCode IntelliSense's quick info feature*

A git repository could host the app code, where e.g. each commit would represent a step in the tutorial, so that the user can compare his code to a reference. The tutorial should recommend best development practices (e.g. laid out as side notes).

Writing the tutorial should also be used as a chance to improve the usability of the Tabris.js documentation.