very basic, needs testing.
* To do: Set switch to reflect the current state on init. (Currently defaults to off after HA reboot.)
* Occasionally the custom component fails to load on HA start. Usually fixed by restarting HA.
* When switches are toggled occasionally a false error is reported. This could be due to async call. The desired behavior still occurs though.
- add total and pending sensors for BTC
- add total and pending sensors for currency
- default currency to USD
- only support EUR or USD currency
- in addition to BTC
- ignore non-BTC exchange rates