- /sync/meta now returns a dictionary
- it includes the following extra fields
- msg: if non-empty, show this message at the end of the sync
- cont: if false, show above message and abort sync
- uname: the user's email address, so it can be stored by the local client to
show users who have forgotten which email address they used. in the future
this will be saved only when logging in, so do a conditional access on it
