Geographic north arrow orientation marker

[banesullivan]

When plotting geographic scenes, a north arrow is often preferable to the typical right-hand-rule orientation marker.

These changes add a convenience method to add an orientation marker that is a in the style of a tradition geographic north arrow.

I somewhat arbitrarily chose the default color of this and I'm not totally loving it -- would appreciate suggestions for better colors.

import pyvista as pv
from pyvista import examples
terrain = examples.download_st_helens().warp_by_scalar()
pl = pv.Plotter()
pl.add_mesh(terrain, show_scalar_bar=False, cmap='gist_earth')
pl.add_north_arrow_widget()
pl.show()

[banesullivan]

This may be better as an example mesh rather than a tool here

[tkoyama010]

Personally, this looks tool.

[codecov]

Codecov Report

Attention: Patch coverage is 95.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 96.96%. Comparing base (06e7a8f) to head (cb27627).

Additional details and impacted files

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##             main    #6070   +/-   ##
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  Coverage   96.96%   96.96%           
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  Files         141      141           
  Lines       24532    24551   +19     
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+ Hits        23788    23807   +19     
  Misses        744      744