Pre: Point at latest dev servers.
Bug 958893 - Pre: Add FxAccountUtils.unwrapkB.
Bug 958893 - Part 1: Round out FxAccountClientRemoteException.
Bug 958893 - Part 2: Add FxAccountLoginStateMachine.
Bug 958893 - Part 3: Add StateFactory.
Bug 958893 - Part 4: Use State and FxAccountLoginStateMachine.
Bug 958893 - Post: Clear preferences when creating a new account.
DO NOT MERGE - Hacky partial commit to sync against 1.5 endpoint.