Added coinbase payout script
Update print statements to use print()
Use instant_buy

We don't keep any escrow in Coinbase, so we always need to buy BTC first
before we can send it along to users as a payout. We do have instant_buy
enabled. Our instant buy limit is $1,000 per week.
Coinbase script now fetches amount and fee from response
Added a note to bitcoin exchanges, and added int/string conversion for fees
Print JSON result if coinbase doesn't give a 200
deduct amount + fee from balance
save elsewhere auth tokens in the DB
add a simplate that uses the elsewhere tokens to refresh the user's data
Update Venmo testing app
Fix bug with 403 code path
Split giving page into two columns if displaying unclaimed tips
Update link to vagrant box per rename
Update Vagrant section of README
Update comment re: rebuilding box
Update Vagrant docs regarding passwords
Merge pull request #2815 from gratipay/update-vagrant

Update vagrant
Merge pull request #2811 from gratipay/split-giving-page-into-two

Split giving page into two columns if displaying unclaimed tips
added recently cancelled tips
Tests for giving page