Description of problem:
Rates in chargeback does not have any unit associated, a rate should include a unit: for instance: €/month, €cent/month, $/month, now it is /month, that is not a rate.

Version-Release number of selected component (if applicable):
5.8.x

How reproducible:
Always there

Steps to Reproduce:
1. Go to chargeback rates
2.
3.

Actual results:
There is the possibility to choose "per time", and "per unit", but there is no way to choose "per currency". In a multinational company, that would mean that you can't differentiate rates in different countries.


Expected results:
A user should be able to choose currency, and create new ones with or without relationship to others.
Currencies should be dynamic, being possible to change a currency in one date (i.e. a currency is applied until the country joins the Eurozone and the € is applied). This could also be configured as a currency that can be applied only in a specific time.

Additional info: