copy Nuclide token
copy Nuclide token

Summary:
* We are now using `flipper.oAuthToken` to store our token in the keychain
* If there is no Flipper token, we copy the Nuclide token (once)
* If the user signs out of Flipper, only the flipper token is removed from the keychain, not the nuclide token
* the Nuclide token is not copied anymore

Reviewed By: passy

Differential Revision: D14598658

fbshipit-source-id: ab0646b35575bd4b2e433d62bb98635f6d127fd2

facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper,facebook/flipper