Restructure plugin controllers and callbacks.

There is now one controller that handles callbacks from Quanto and one
that handles callbacks from Fitbit. As we add 3rd party providers, we
also add new controllers and routes in charge of handling their
callbacks and token creation. Good times indeed.
Restructure plugin controllers and callbacks.

There is now one controller that handles callbacks from Quanto and one
that handles callbacks from Fitbit. As we add 3rd party providers, we
also add new controllers and routes in charge of handling their
callbacks and token creation. Good times indeed.