Fix for #1481: Add Device, DeviceZone, Zone to syncing models.

TItle says it all.  

Because these models are specially transferred during the syncing hand-shake (only if missing completely), changes in data are never sent.

By adding to syncing models, such changes will now be sent.  It's just that easy!

**Testing:**
* Tested after registering to old central servers; nothing breaks.  I.e. this is at least as good as the old.
* After merging, will test further.  This should work just fine, but the change is so small (essentially 1 line), we can easily back out if needed.

@jamalex please take a look by Thursday afternoon, if you have time.