Axes3D.w_xaxis property no longer exists in new versions of matplotlib

[Dominic-DallOsto]

Same issue as NeLy-EPFL/DeepFly3D#50

Since matplotlib 3.1.0 the Axes3D.w_xaxis Axes3D.w_yaxis and Axes3D.w_zaxis properties have been deprecated and in matplotlib 3.9.0 they no longer exist. See https://matplotlib.org/stable/api/prev_api_changes/api_changes_3.1.0.html#axes3d.

We can just replace these with Axes3D.xaxis Axes3D.yaxis and Axes3D.zaxis.