Get current device

[itsjustbrian]

Possible duplicate of #61, but I wanted to open an issue focused specifically on the ability to read what the current playing device is from the SDK, or at the very least, whether Spotify is using the local device or not. This (I imagine) would be a very simple addition that would really help the functionality of my app and I'm sure others' too. #61 is also pretty old at this point and doesn't seem likely to get picked up.