Make the sync between side-service and ZeppOS app interactive 

I think the sync between phone and watch need to be interactive, because when the user changed their phone, 2FA token will be deleted with no warning.
User might lose the access to their account unexpectedly, and even if they had added 2FA toke to another authenticator app, they need to reset 2FA to use this app again. 

p.s I'll make a PR for this. 