clarified iterations: enforce full top_down/bottom_up cycle for better stability of layout;
always swap panels, which leads to slightly better GUI layout;
option graphview_swap_panels;
more explicit Layout.Info: size and content; allow multi-line vertex label, based on content; misc tuning;
configurable options;
GUI.imitate_font: more explicit result size, e.g. relevant for caching; some graphview font options: Helvetica family is important for self-contained PDF; tuned;