Improve caching by normalizing date ranges

[runningman84]

At present the date filter is very exact, this prevents effective caching of requests.

My timefilter is "a month ago" to now. The request to ES is different every new second. In order to cache these requests in nginx for 10 minutes the from date should not change until another 10 minutes passed by. Especially for time ranges greater than a few hours this would not change the output dramatically but would greatly help us... Maybe this setting could be configurable.

                      "range": {
                        "histogram_time": {
                          "from": 1381744215109,
                          "to": "now"
                        }

[bobrik]

See #625. If you create indices daily you don't need range filter in most days.

[rashidkpc]

This wouldn't really work as some systems have things indexed into the future. #625 is probably where the improvements will happen. As well as elasticsearch's new query cache.