FeatureBased: plot_feature_3d plots feature 2 on the z-axis; second 3D plot has mismatched axis labels

[jonfroehlich]

Found in the #16 correctness/prose/comments audit (verified against plot_feature_3d's source).

Two related bugs in the 3D feature-exploration plots in GestureRecognizer-FeatureBased.ipynb.

1. plot_feature_3d never plots the third feature. In the helper (cell defining plot_feature_1d/2d/3d):

x = list(extract_feature_func1(trial.accel) for trial in trials)
y = list(extract_feature_func2(trial.accel) for trial in trials)
z = list(extract_feature_func2(trial.accel) for trial in trials)   # <-- BUG: func2, should be func3

extract_feature_func3 is accepted as a parameter but never used, so the z-axis duplicates the y-axis — every "3D" scatter is secretly 2D-on-a-diagonal. Fix: z = list(extract_feature_func3(trial.accel) for trial in trials).

2. Mislabeled axes in the second 3D call. The cell plotting std_mag, max_mag, num_peaks_mag_p passes axis labels copied from the previous cell:

plot_feature_3d(selected_gesture_set, extract_feature_std_mag, extract_feature_max_mag, extract_feature_num_peaks_mag_p,
                xlabel="top_mag_freq2", ylabel="max_mag", zlabel="std_mag", ...)   # <-- labels don't match the data

The title ("Std mag vs. max mag vs. num peaks mag_p") is right, but the labels should be xlabel="std_mag", ylabel="max_mag", zlabel="num_peaks_mag_p".