Show human readable error message if backend requests fails

[Sebobo]

F.e. when there is a privilege problem (error 401) then it should recommend to log out and in or something like that. Error 500 and any other error should have a meaningful message.

[creative-resort]

I just stumbled upon this, after installing the package while logged in. My expectation was for the existing login to be sufficient and any additional authentication to be taken care of for the user automatically, so that a re-login wouldn't be required.