Guest cart replaces authenticated with its content

[VitaliyAdamkov]

Guest's cart should merge into the current order after authentication like after regular sign in via email & password.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[fthobe]

@jarednorman i believe we closed this, maybe you want to take a look.