Display error on invalid credentials action

Hello,

When I was trying to save articles I got the message "An error occurred while saving the article" very quickly.
It was working and then stopped recently.

I soon after realized that it's because the extension wasn't getting an api token because I changed my password not long ago.

I just thought I'd suggest it might be nice to give a more descriptive error message if possible. Perhaps something about the token not being granted and maybe even open the setting page for the user.

Anyway, thanks for all your work on this extension I love it :)