[Feature] - Refund System

[Paulsenik]

Is your feature request related to a problem? Please describe.
When misclicking an item can't be refunded without an admin stepping in.

Describe the solution you'd like
A small button in the ui to revert the last transaction for the next 10-30 seconds.

A new transaction of type REFUND will be created. The according itemhistory-entry now links to the initial buy-transaction and this new refund-transaction.