UX When flashing unsupported / unknown models

[yanosz]

Is:
As disucssed on IRC: Flashing the file for the 7362 SL resulted in error_temp(resp)ftplib.error_temp: 426 Data connection closed, confusing the user. --image was specified on the command line.

Background:

• The 7362 SL is not supported, thus the installation fails.

Better:

• A workflow on unsupported hardware could guide unexperienced users to avoid flashing using fritztools, thus providing a safe default.
• A easy-to-read error error could be shown instead of error_temp(resp)ftplib.error_temp: 426 Data connection closed
• The exact consquences of --image and -f could be documented at https://fritz-tools.readthedocs.io/en/latest/