Feature/auth bloc error handling

[micahmo]

Pull Request Description

This PR adds instance/network error handling to the AuthBloc so that we can detect issues as early as the first API request (that is, checking for downvotes enabled).

Note that this does not replace the similar handling in the CommunityBloc.

This PR supercedes #769.

I also updated some timeouts throughout the app to be more consistent.
I also added a new helper method to translate exceptions to messages.

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

qemu-system-x86_64_VppEu146vv.mp4

Checklist

• Did you update CHANGELOG.md?
• Did you use localized strings where applicable?
• Did you add semanticLabels where applicable for accessibility?

[hjiangsu]

Looks good! Sorry again for introducing this issue with my previous feature for checking instance downvotes 😅