Add ignore-invalid option

[Scrumplex]

By default wob exits when invalid input is read from stdin. Some users
might not want wob to exit here. This adds a runtime option that
controls wether wob will exit or just skip the input and wait for the
next input instead.

This PR adds a new runtime option (-i or --ignore-invalid) to just continue as usual if invalid input is sent.

This could be useful in case some script misbehaves, as the user will still get future feedback and can continue their work.

[francma]

I've cherry-picked the two fixes into master, thanks for that.

I don't like the new option. I think it is not that hard to produce script that feeds wob with valid values. And once the script is written, it's highly unlikely that it will randomly break.

[Scrumplex]

And once the script is written, it's highly unlikely that it will randomly break.

Yes that's probably fine as well. I will close this then