Add timestamp column in payment_transactions
Add helper to retrieve latest transaction
Add new transaction status: cancelled
Store/retrieve registrant paid status to/from table

* Add payment toggle button in registrant modification page
* Remove registrant payment modification page
Add provider column in transactions table
Delete transactions when registrant gets deleted
Add padding in material infoline
Beautify layout of checkout page
WIP: Add payment confirm/cancel/notify handlers
Easier build of the source version on Python 2.6
Remove payment notification RH/blueprint