Support auto-login to YaCy

[JeremyRand]

YaCy by default requires all users who aren't coming from localhost to log in in order to start crawls. The login operation is an HTTP POST. For such users, this script will fail unless they've manually logged in prior to browsing sites that they want to index.

It would be useful to handle this better.

• Detect the case where YaCy requires a login.
• In such cases, if user hasn't configured login data, prompt the user for it.
• In such cases, if user has configured login data, automatically log in to YaCy.
• If the user's configured login data is rejected by YaCy, notify the user and allow them to fix it.

Thanks to zeeand00 on Freenode IRC for pointing this out.