Include "passup update" functionality in "passup" command

[alanchrt]

Should we just make it so the adapters get updated every time "passup" is run? That way, people don't forget to update each time and have a bunch of them fail because they're outdated.

[coalman]

Yeh, I think it flows better that way. Perhaps passup could check whether there are updates on the master branch and ask the user if they would like to update?

I've also been wondering about error resolution. If multiple passwords in a group get updated but a few fail, should we offer to rollback the changes on the other sites in that group? Not really sure about this idea tbh.