Migrate Android app from Webview Gold to existing expo.dev project

[joergreichert]

Current state: Android app last updated two years ago, at those days WebViewGold was used.

Motivation: Since last october there is also an iOS app available built using expo.dev Code is shared here: https://github.com/CodeforLeipzig/leipziggiesst-expo This very same project can be also used for building the Android app. So for streamlining development this should be done, especially when later we want to switch parts of the app to native components and use notification mechanisms.