LP#1789679: Provide ROLLUP support in report output

LP#1789679: Provide ROLLUP support in report output

In Postgres 9.5 and newer, it is simple to generate group subtotal and grand
total rows for aggregate queries. The simplest thing would be to spell the
grouping clause as

  GROUP BY ROLLUP (...)

rather than

  GROUP BY ...

when there is a mix of aggregate and non-aggregate columns in a report.  This
branch does just that.

The report definition UI now has a checkbox labeled "Calculate grouping
subtotals" which enables use of the ROLLUP functionality.

Signed-off-by: Mike Rylander <mrylander@gmail.com>