WIP: add donations page to the scipylib area of scipy.org

Not ready to merge, still needs discussion on scipy-dev. I did send a message asking feedback on listing sponsors (http://thread.gmane.org/gmane.comp.python.scientific.devel/17859) but no responses to that. Donations have not been set up or discussed yet.

Given that other scipy stack projects can and in some cases do have their own donations pages, and there's NumFOCUS for ecosystem-wide donations, I chose to put this page under scipylib/