Switch iOS universal link from irma.app to open.yivi.app

[ivard]

We want to phase out the IRMA name in the links where possible. Therefore, we want to switch the universal links to open.yivi.app. We chose a separate domain to enable us to add a universal link fallback application that helps the user to download and configure the app.

For Android, we stick to the intent:// link because Firefox for Android app and some WebView implementations always open universal links in the browser instead of opening the app.

Note: ensure that all app versions <7.5.1 are phased out using the required update mechanism first. In 7.5.1 we introduced the open.yivi.app universal link in the Yivi app. The minimum app version is specified in the scheme. If the user's app is older than the version recorded there, the required update screen is being shown. The build number of 7.5.1 is 4194465.