Dev/layouts - #251

g = graphisty.edges(pd.DataFrame({'s': ['a', 'b'], 'd': ['b', 'c']})
g2 = g.materialize_nodes()
g2._nodes  # pd.DataFrame({'id': ['a', 'b', 'c']})

g = graphisty.edges(pd.DataFrame({'s': ['a', 'b'], 'd': ['b', 'c']})
g2 = g.get_degree()
g2._nodes  # pd.DataFrame({
           #  'id': ['a', 'b', 'c'],
           #  'degree_in': [0, 1, 1],
           #  'degree_out': [1, 1, 0],
           #  'degree': [1, 1, 1]
           #})

g = graphisty.edges(pd.DataFrame({'s': ['a', 'b', 'c'], 'd': ['b', 'c', 'a']})
g2 = g.drop_nodes(['c'])  # drops node c, edge c->a, edge b->c, 

g2a = g.tree_layout()
g2b = g2.tree_layout(allow_cycles=False, remove_self_loops=False, vertical=False)
g2c = g2.tree_layout(ascending=False, level_align='center')
g2d = g2.tree_layout(level_sort_values_by=['type', 'degree'], level_sort_values_by_ascending=False)

g3a = g2a.layout_settings(locked_r=True, play=1000)
g3b = g2a.layout_settings(locked_y=True, play=0)
g3c = g2a.layout_settings(locked_x=True)