Add a manifest.json to make Cesium a native app in Android

Information taken from this link: http://frank.taillandier.me/2016/06/28/que-sont-les-progressive-web-apps/

To understand what I am talking about, you can visit https://forum.duniter.org with an Android phone and select the option "Add a shortcut to the HomeScreen" (Ajouter à l'écran d'accueil) to have the forum as a "native app".

If you click on the newly created shortcut, you can see the forum opened like a native app, however it is opened in a fullscreen mode without the browser toolbars.

Like a native app.