Activity "group by date" should ignore time

http://dev.nysenate.gov/issues/9661

From Brian:

The issue came up that when grouping by activity date in the activity report, it groups by date and time – which for all practical reasons is pretty useless. it's highly unlikely you would have a large set of activities created with the exact same time. even if you bulk-created a large set of activities, it's very possible they will extend over a couple seconds. it's much more reasonable to expect that the grouping would happen by day, irrespective of time. I think this is an issue that just makes sense to change in core.