Add methods for cart JSON serialization
Use JSONSerializer for session serialization. Use latest satchless version
Serialize Address objects to JSON
Store serialized cart in session
Create Cart object only when its needed
Store dicts in cart
Fix template variable names
Basic SessionCart implementation with tests
Construct Cart on base of serialized SessionCart
Fix tests
Remove unused methods
Store SessionCart instance as request.cart
Change template variable names for Cart
Remove unused methods
Revert "Remove unused methods"

This reverts commit 156e50ea58bbf5c6e51c1b4de3205dfa47d1157e.
Clean up unused test
Don't implement whole cart API in SessionCart
Template variable names improvements
Remove print
Apply code design suggestions