Implement email notification for TAN challenges during an automated run

[Bur0k]

During an headless import (GET Parameter automate and config set) it can happen that a TAN challenge is posed. In this case the user usually doesn't sit in front of the browser or terminal.

Therefore an email notification can help and this PR implements this.
The configuration required for this to work is in the .json under the tan_required_email_notification object (See example.json). All fields are required to be non empty, else the email notification won't be enabled.

Question:

1. I didn't want to save every email config entry in the session. Therefore I just reread the configuration file. Is this fine?

solves #75

[Atlasfreak]

Would be a really nice feature. If you don't regularly check if all transactions are there it is hard to notice that the TAN expired. Additionally I don't know if a bank would block you after sometime if you try to login with a expired TAN too often.

[TyrionWarMage]

I'm using this in production for quite a while now. Didn't have any issues. Imho, this could be merged.