Pricing model bills same amount of X regardless what currency is X

[Nuanda]

At the moment, if you have GBP fund, and a flavor hourly cost is 5, you are going to pay 5 GBP per hour. But if you have PLN fund, you are going to pay 5 PLN per hour.

Possible solutions:

• set all hourly costs in specific currency and support currency exchange rates
• limit fund currencies to the one used (implicitly) by hourly cost (we may even call it some artificial name, like Atmosphere Billing Units)
• (less interesting) set different hourly costs per currency.