Move settings tabs definitions
Use properly Customer entity as source for addresses
Move addresses into Customer class
Use tax address for shipping tax
Add billing and shipping fields
Implement cheque payment gateway
Implement on delivery payment gateway
Add displaying messages in settings
Implement free shipping gateway

Additionally added better validation for flat rate
Add/remove shipping methods based on product subtotal
Add checking for proper shipping method
Add checkout validation
Add server-side address validation
Fix shipping method changing
Add "Thank you" page
Add "Pay" endpoint (without support)
Add checkout Ajax actions, add proper changing country in checkout