Uncouple the currency of the purchase cost from device location

[SJL-369]

Currently the currency of the purchase cost is linked to the location of the device/user, e.g. a device located in UK will show it's purchase cost as GBP, a device in the US will show as USD, etc.

The problem is when the device is assigned to a user that's in a different location. This will change the currency to the user's location, e.g. a device that cost GBP 1000 will change to USD 1000 when it's assigned to someone from the US. This obviously creates an inaccurate record of the cost.

Can we have the currency uncoupled from the location? Perhaps have it as a standalone property, or link it to the supplier rather than the location?