First pass at a masspay script
Split masspay script into a couple steps

I didn't like posting to Gittip in the same loop as I was computing the
CSV to upload to PayPal. I want a little more control over the process
at this point.
Merge branch 'master' into masspay
This adds a participants.paypal_email field

The purpose of this field is to record a PayPal email address for people
whom we're paying out via MassPay. Since MassPay isn't intended as a
long-term option, I'm proposing that we don't need a UI for this field.
I'll update it manually via psql as needed. Generally I hear from people
on support@gittip.com. I confirm the email address manually by asking
for the first eight digits of their API key.
Remove redundant variable initialization
Add a docstring to masspay.py
Make the masspay script a little more flexible

Take the Gittip instance URL from config to enable the possibility of
testing.
Merge pull request #1582 from gittip/masspay

MassPay