Default delta

Checking the current status of datagrepper, we realized that not specifying a delta value in the URL led to timeouts while specifying one, makes datagrepper return properly.

Investigating the configuration options of datagrepper, we found out that there is a DEFAULT_QUERY_DELTA configuration key that allows to specify a default delta value when one is not specified.

Just setting that configuration key to 60*60*24*3 (ie: 3 days) improves the datagrepper performances quite a bit (as in queries actually return instead of timing out).

That configuration change, does break the API a little bit as with it, it will limit the messages returned to the last 3 days.