Update FxA client and manager with latest gecko changes
Use FxAccountsClient
Remove the intro screen, that goes in the FTU
Use the same logo in the FxA manager as the FTE.
Hook up to the FxA client!

* Start to hook up error screens based on responses.
* Rename FxModuleServerRequest->checkPassword to signIn, and createAccount->signUp
Start to generalize the error handling.

* Create fxa_errors.js which converts error responses to strings
* Add showResponse in fxa_error_overlay.js which shows error responses.
* Start to unify how all errors are handled.