Add the about page in the demo app

[B3nz01d]

Context

Issue 1

As a user of the demo App
I Want to know understand the context of the app I'm using
So That I can see:

• the type of the app (Alpha / Beta / Prod)
• The version of the app
• the privacy policy
• the legal information
• the accessibility statement
• which version of the token is used in the app and check the latest updates of the token with the reference version correspondance that is logged in the about page of the demo app

Issue 2

As a user of the documentation
I Want to know which version of the token is used in the library
So That I can check the latest updates of the token with the reference version correspondance that is logged in the documentation

Description

Issue 1

In the demo app there should be a standard list that proposes the following link or items:

• the app name:
  "Orange Design Toolbox"
• the version of the app:
  "Alpha Version 1.1.1 (build number)"
  nb: the info of "Alpha" should be either showing for "Alpha" and "Beta", but nothing should show for the prod version
  so you would have the following cases:
  • Alpha: "Alpha version 0.1.0 (450) - Issue # 278"
  • Beta: "Beta version 0.1.0 (450)"
  • Prod: "Version 0.1.0 (450)"
• the token file version:
  "Token version: v1.0.0"
• the app description:
  "In this app you'll find the implementation of the Orange Unified Design System library for Flutter with descriptions and code examples of the tokens and components"
• "Change log": a link to the corresponding page
• "Privacy policy": a link to the corresponding page
• "Terms of Service": a link to the corresponding page
• "Accessibility statement": a link to the corresponding page

Issue 2

Also on another note, make sure the token file version is included in the pages of the documentation pages that refer to the tokens