Adding robots.txt to fix random 404 message

This fixes the randomly appearing 404 error in Auth (issue #1232 (closed))

I encountered this issue with the random 404 message in several auth systems, which doesn't stop AA from working, it's just annoying popping up every now and then. To all these system I added the robots.txt quite some time ago and the 404 never appeared again.

So here we are, with a robots.txt ...