Offline mode for non network connected devices

[GamingGuy003]

An offline mode would be useful for people running the tool on an isolated device (Raspberry PI, Nuc, whatever...) without an active internet connection.

The easiest way to detect if the tool should run in offline mode is to check , if the initial update check fails. Should this happen, we can safely assume the user does not have a working internet connection, and we can ignore further update checks. We can also disable all other online functionality (greying out the update button, etc.) until the tool is restarted

This can reduce potential delays, should the tool try to download updates which it will never be able to receive etc.

[Benji377]

Todo for me:

• Make the update button inactive when the user has no internet connection
  (I forgot to do this in the last release 🙃 )

[GamingGuy003]

Scanning seems to function only occasionally when offline

[Benji377]

@GamingGuy003 fix the check_update function to work in offline mode

[GamingGuy003]

should have been fixed using with cca9cad

[Benji377]

@GamingGuy003 you can close this if it works now.

[GamingGuy003]

Still needs testing on iced but after that yes

[Benji377]

I can confirm it works very well on Windows 11

[GamingGuy003]

Completed with new downloader