- `GetCashBalance()` will return a `List<CashAmount>`, will not need to
set conversion rates, which requires knowing what the account currency is.
- Removing `Global.Holding` conversion rate field. It wasn't being used
and required knowing what the account currency is.
- Adding equality operators for `CashAmount`. Adding unit tests.
- Moving `UniverseSelection.EnsureCurrencyDataFeeds` call into the
`IResultHandler` implementation through usage of the new `SetupHandlerHelper`
class, that will also set an initial conversion rate if none present.
- Adding regression test, that reproduces original issue
- Completly move `DataManager` in front of `DataFeed`. Specifically
`AddSubscription()` and `RemoveSubscription()` implementations. Also
removing IDataFeed.Subscriptions
Stefano Raggi