Start storing currency codes alongside a bool marking it as crypto or fiat to avoid conflicts

[einsteinx2]

Right now we don't specify that a currency is crypto or fiat, we just assume if it doesn't match a fiat code then it's crypto. However there are at least two fiat currencies that match crypto symbols (Solomon Islands Dollar [SBD] and Saint Helena Pound [SHP]). In these cases, the currencies are obscure and can just be removed from our enum, but it would be best to specifically mark currencies (both in the exchanges rates data as well as local app data) as crypto or fiat. Then we can enable all fiat currencies and not worry about conflicts. For now this is fine as the conflicts are only with currencies unlikely to be used by our users, but in the future as there are more and more crypto symbols this will be the best solution I think.