Fix style for colored buttons in toolbar
Add registration toolbar in event overview

close #1661
Post-WIP fix
Fix authentication error when clicking 'Checkout'
Change grouping of 'Get ticket' button
Fix trying to access avatar object when not logged
Improve registration toolbar in event overview
Add permalink to non-logged registration page
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