Improve color handling and documentation of plot_neighborhood

[schroedtert]

• Fix bug, that the color could not be set as expected
• Forward walkable area options correctly
• Improve documentation, state clear what base and default pedestrians
  are
• Add options to control alpha of default, base, and neighbor
  pedestrians
• Add options to print without walkable area

from pedpy import plot_neighborhood

plot_neighborhood(
    pedestrian_id=5,
    voronoi_data=voronoi_data,
    frame=0,
    neighbors=neighbors_single,
    base_color="red",
    base_alpha=0.7,
    default_color="blue",
    default_alpha=0.2,
    neighbor_color="green",
    neighbor_alpha=0.5,
    walkable_area=walkable_area,
    line_color="magenta",
    line_width=5,

).set_aspect("equal")
plt.show()

Closes #465

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.33%. Comparing base (65afabb) to head (73e53fe).
⚠️ Report is 29 commits behind head on main.

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