Bugfix: plot legend is clipped in scatter_by_dge_class outputs #313
Description
Plotterlib's ScatterCache constructs a figure using a layout engine specification that is no longer compatible after the recent update to Matplotlib 3.7 (#307). This means that the legend in scatter_by_dge_class is clipped because the axes object is centered after expanding the figure rather than remaining fixed in place. The other scatter plot outputs are also produced with less margin than they had before.
