Fix website and description for scipy easyconfigs

Previously, all the scipy easyconfigs listed numpy.org as the homepage
and used a copy-pasted numpy description with "Numpy" replaced with
"Scipy".

This commit changes the homepage to point to scipy.org and changes the
description to that used at the beginning of the SciPy reference manual:

"SciPy is a collection of mathematical algorithms and convenience
functions built on the Numpy extension for Python."