Streamline credit balance transfer from admins to users and back

[novoselt]

At the moment admins can "buy" vouchers at the store without paying for them and then send these to the users. They also can redeem these vouchers themselves impersonating a user. And it is possible to impersonate a user, buy a voucher, and then redeem it as an admin to decrease user balance.

It would be better to enter the amount and user email address in the admin interface, press a button, and have that amount added or removed from the user credit balance, while also getting a matching record for the admin account. It is highly desirable to have "zero total" for each transaction as with financial ledgers.