Provide for accounts that lack a SpiderOak Hive folder:

* If the account's content lacks a 'syncfolder', indicate in the hive
  model object that the hive is absent.
* If the hive model shows that the hive content is absent, inhibit the hive
  presence in the UI, pushing the devices view as the default, instead.

There may be better ways to inhibit the hive UI artifacts, but the presence
of the hive in the UI now depends on whether or not the account has it.