Add group color edges for better clarity

Here is Qtile graph, rendered with the following settings: ``` [dbs] aspect_ratio: 1.5 font_scale: 0.4 font_color: #000000 edge_color: #c5c5c5 img_y_height_inches: 8 dpi: 300 color_map: autumn color_scatter: 0.0 top_level_spacing: 10 min_node_size: 1 max_node_size_over_min_node_size: 50 add_size_per_out_link: 2 max_displacement: 100000 num_iterations: 100000 tmax: 100 y_sublevels: 6 y_sublevel_spacing: 0.3 attractive_force_normalization: 8.0 repulsive_force_normaliztion: 6.0 ``` I believe having colored edge based on a local group (or level?) could greatly benefit the readability of the graph