About mahotas dependency

[dipaco]

I think we can emulate the behaviour of bwperim with:

from skimage.measure import find_contours, grid_points_in_poly
C = find_contours((I > 128).astype('uint8'), 0.5)
si = np.argmax([a.shape[0] for a in C])
G = grid_points_in_poly(I.shape, C[si])

And this way delete a dependency on the code from which we only use one function for the moment. Off course, if we see the need to use mahotas again, we should reconsider to use it.