New Deployer should prompt for username/password if necessary

If the deployer connects to the server but gets an authentication error, and a username and/or password was not passed on the command line, it should prompt for them and try again.

Ideally, we'd figure out how to make the password typing invisible – I have hope that we could use similar code to what Maven does when it updates the download progress, but I really have no idea. I expect this can be broken off as a separate issue once some sort of prompting is working.