graphics/py-scour: add new package

Scour is an SVG optimizer/cleaner written in Python that reduces the
size of scalable vector graphics by optimizing structure and removing
unnecessary data. It can be used to create streamlined vector graphics
suitable for web deployment, publishing/sharing, or further processing.

Packaged in wip by K.I.A. Derouiche, imported mostly verbatim.

(gutteridge)