Add index to make statistic compilation scalable
Add index to make statistic compilation scalable

The statistic compilation for the resources did not scale. There was too
much data for sort() in MongoDB. Hence, I have added the appropriate
index.

Signed-off-by: Konrad Reiche <4ff0213f56e2082fcd8c882d04c546881c579ce4@gmail.com>

platzhirsch/metadata-census