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.