Auto sync: add login approve reuqest notification

Currently, I have to manually click the “Sync Now” button or perform pull-down gesture to sync everything, including sync login approve requests. Whenever I need to approve another device, I have to first find and open the app, then sync manually, then wait to see the request page, then finally click the “approve”, this is a bit troublesome.
App can start a sync service on the background, so that the vault will be “always” up to date, and can when other device request login, a notification message will prompt up, so that we can approve it with it, it can be a simple message without buttons, which will open the app by clicking it, or can be an advance message with “Approve/Ignore” buttons (and passphrase), which can be more friendly.