Drop online web clients support #80
Description
The goal is to keep only the built-in web clients supported for the following reasons:
- Enhanced app security. Built-in web clients are static resources built from the official source code repositories and come prepackaged with the app installation package. So email provider can't ship to you intentionally or not a malicious/hacked web client version.
- Enhanced app stability. The app is more stable in case of built-in web client used since it doesn't depend on the online web client being independently updated and deployed by Protonmail / Tutanota dev teams. See here and here examples of how the email provier's breaking changes happened before affected the app.
When the app with this feature implemented gets started, it will automatically convert used online accounts to the built-in web client version. In order to go that way I will probably need to enable built-in web client for the https://app.protonmail.ch domain too in addition to already enabled https://mail.protonmail.com and https://protonirockerxow.onion domains.
I think that will be ok to keep online web client enabled for https://beta.protonmail.com domain only as beta users are prepared to face possible issues happening.