Refactor BarTop Singleton's use of accessToken

[jamesvclements]

For authentication, the BarTop API singleton relies on the users' accessToken. When the user logs in, we set that token in our authentication redux state. But we want the BarTop API singleton to have access to it.

It would be repetitive to pass in the token from the state for every authenticated API call. We'd have to make every authenticated a thunks so it could use getState, and then dispatch the [CALL_API] actions and pass the token.

But because the accessToken is synced with storage, the BarTop API singleton needs to also read storage & keep in sync with our redux state, which is lame.

I'm not sure the best solution for this yet, but I'm sure there's something cleaner than that second option which is what we're doing now.