[FEA] tree layouts should support a planar layout mode

[lmeyerov]

Is your feature request related to a problem? Please describe.

When plotting tree data, edges sometimes intersect. Ex:

g = (g
     .get_degrees()
     .tree_layout(
        level_sort_values_by='degree',
        level_sort_values_by_ascending=False,
        level_align='center',
        vertical=True,
        ascending=True)
     .settings(url_params={'bg': '%23' + '000000', 'edgeCurvature': 0.05,'edgeInfluence': 1.5,'pointSize' : 0.5})
     .layout_settings(play=0, locked_x=True)
    )
    return g.plot(render = False,memoize = False)

On planar graphs (ex: trees), this should be avoidable

Describe the solution you'd like

The default should be something like sort-by-parent-position (level_sort_mode='parent'?), which can be used if level_sort_values_by is not set

Describe alternatives you've considered

• radial versions of the same
• implement / embed reingold tilford (tidier) (ex: https://hci.stanford.edu/courses/cs448b/f09/lectures/CS448B-20091021-GraphsAndTrees.pdf)