[Feature request] Telegram Auth: Skip Channels where the bot isn't a member

[TechG3n]

Expected Behavior

If the Bot isn't in the specified chat, post a warning and check the next ChatID

Current Behavior

It get's stuck if the bot was removed from one group and won't let new users authenticate

Possible Solution

Skip chats where the bot can't read the members

Steps to Reproduce (for bugs)

1. remove bot from a chat which is specified in the config
2. logout from map and try to login again
3. Site loads infinitly and log shows "Exception while retrieving Telegram data: 403 Client Error: Forbidden for url: https://api.telegram.org/bot11111:2222222222222222222/getChatMember"

Context

One user removed the bot by mistake, allready logged in users are fine but new ones can't login

Your Environment

• Version used: newest pull
• Environment name and version (e.g. Python 2.7): Python 3.6
• Operating System and version (desktop or mobile): all