Activity detail report: group by date

When grouping by activity date in the activity detail report, the grouping happens on both the date and time value. while the timestamp is important when looking at the activity records themselves, it's not particularly helpful when grouping, as there ends up being many time-specific groups for a given date.

we will look at modifying the grouping behavior for this particular field so that we only consider the date value.

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