Rectangle::addToBottom or supporting negative values in removeFromBottom

Feature Requests
#1

It may be nice to build a viewport’s contents like this:

Rectangle<int> b;
b.addToRight (500);
for (auto& row : rows)
    row.setBounds (b.addToBottom (50));
container.setBounds (b);

Rectangle::removeFromBottom with a negative value almost does what addToBottom would do, but the resulting rectangle is incorrect.