Fix run seeds when offline

[eugenk]

Seeds depended on an internet connection. With this change they don't:

• Proof statuses and categories have fixtures. They are only used if the download from ontohub.org failed.
• Oops is skipped if either a SocketError (no connection at all) or a RestClient error (e.g. 404 or similar) occurs.

In both cases a message with the error is printed to stdout.

[eugenk]

As requested in the meeting yesterday, I changed the default behaviour to use the local fixtures only. By setting an environment variable (DOWNLOAD_FIXTURES), we can choose to use online files from ontohub.org instead. The rebuild script sets this environment variable if the -d option is supplied.

Also, -i makes the rebuild script only restart invoker and not clean the state.

[0robustus1]

I'd prefer -r (for restart) instead of -i (for invoker, i assume?).

[eugenk]

Renamed with 51bed36

[0robustus1]

Please use the <<-MSG way and indent the closing MSG correctly.

[0robustus1]

👍