Warn user through a popup if solidAuthenticate fails

[gjwgit]

Description

When the server is down I get the following message on the console, but no indication in the app

solidAuthenticate() => solid_auth.authenticate(https://pods.solidcommunity.au)
Solid Authenticate Failed: HttpRequestException(502): 

Can SolidLogin catch this exception and display amessage: Unable to authenticate with the server. The server may be inaccessible or down.

Why

So that as a user I can get a clear indication that something is wrong and how to fix it.

Closing Criteria

Checklist for closing the issue:

• No errors from make prep
• All tests pass make qtest
• The authentication exception is caught
• The user is informed

Alternatives

The console message is okay but when running the released version the suer of the app wont see that.

Additional Context

[tonypioneer]