Teach masspay.py to use new paypal_fee_cap field

Rel. #1675
Change a flag to fit my brain better

I always try masspay.py -p, and the user is always right! :-)
Drop interactive CLI entirely

I never use it. Instead let's just point to the command line switches.
Here's a report to help with escrow balancing

Over on #1988 I've done some more thinking about how to manage our
escrow across our multiple accounts. This adds a report to the masspay
script to help make decisions about that.
Better PayPal penny testing
Here's yet another attempt to placate PayPal

It turns out there's another twist to the MassPay penny saga: in some
situations (when amounts are small enough?), the fee is rounded to what
we wanted it to be anyway. See #2296 for a description.

This commit takes a whole 'nother approach to fee computation. Instead
of computing / 1.02 of the target and then fudging it from there, we
take a much simpler approach. We start at a penny under the target and
work down from there a penny at a time until we find a value that works.
Less efficient but safer.
Merge pull request #2298 from gittip/eat-even-more-pennies

eat even more pennies