Add functions for doing morphological operations assuming spherical strel

[jgostick]

I wanted to use scipy.ndimage.binary_opening today only to realize I need to create a structuring element, which requires N more steps to import this and that, which in turn requires looking things up. Slightly time consuming and rather annoying. It would be way easier if there were functions which just accepted im and r, assumed a spherical strel, and just did it.