Adding billing postal code, fixing billing statement text, improving logging

Pretty big PR:

1) We now require billing postal code on checkout, which should help reduce the number of failed transactions.  The field accepts between 3 and 10 characters to accommodate international postal codes.

2) The billing statement text feature has been updated to pass the text on campaign creation instead of on each payment

3) Finally, we bumped up the logging level for key events (namely interactions with the crowdtilt api) to info, and set the logger to print to STDOUT, so that we can track everything better in heroku logs