pre-populate index.yaml

Minimal index definitions for vanilla gae-init are used so the zigzag
algorithm can do the rest. Tested with the changes introduced by #201 and #215.

implements #208, closes #210 and closes lipis/gae-init#6.

To summarize, I was wrong when I suggested that the ```index.yaml``` will be ignored after it is added to .gitignore
+1 for this PR