Reports & charts — Filter the groups, not just the rows

An ordinary filter narrows the records — “amount is over 10,000” keeps the big deals. A group filter narrows the groups: “only the regions that billed over 10,000”, which is a different question and was previously unaskable. It uses the same builder and the same operators, because a grouped row is still a row — its values are the aggregates in each column. Groups are dropped before anything else is built from them, so the totals at the foot always add up to the rows above, and a column that empties disappears from a cross-tab rather than lingering with a total nothing accounts for.