* Add #purchase to Credit
* Assigns spent credits to the listing
* Add Credits::Ledger and use it
* Localize ledger datetimes
* Add organization to the ledger
* Add tests for ledger
* Remove unused class
* Fix scope error
* Compare UTC times
* Fix broken specs
* Wrap listing create in a transaction
* Wrap listings bump into a transaction
* Avoid microseconds issue with datetimes in tests
* Use .detect instead of .select.first
* Fix spec description
