Wrote a template saving convenience function.
borrowed 'inNd' function from Stack Overflow

(N-d analog of np.in1d, I think it only works for integer data, but it's PERFECT for what I need: testing collisions of 3d indices)
Added `verbose` kwarg to `load_template`
wrote `inNd_indices` & added docstring to `inNd`
Wrote `reconstruct_selections_from_template` and it seems to work!
Wrote `reduce_selection_to_principal_branches()` (long overdue!)
Draft template analysis code - pretty basic but functional for demos
Improved how the template analysis works.