Change the scale fitting code from 2 pass fit to a 2.5 pass fit. The fit function is now passed a margin object that contains the margins on the left, top, right, and bottom of the scale. This is useful to know if you can draw outside of the width. This is used by the dataset scale so that extra padding is only added for long labels if absolutely required. If there is unused space underneath the vertical axes, that space is used first.