start to implement cart creation process
put getCart into action classes
allow to create new cart
add some phpdoc
create InvalidCartException
Session::getCart return a Thelia\Model\Cart instance or null if cart is
not valid
refacto cart process
initialize cart test
complete cart test
remove use statementnot needed
finis test for cart creation
change visibility for property in cart test
start test for session class
finish session test for cart part
fix endlife cookie cart
add some phpdoc
Merge branch 'cart'

Conflicts:
	core/lib/Thelia/Core/HttpFoundation/Session/Session.php