Added checks and filters when retrieving ApiKeys from the database to ignore those whose connector types not supported in the current codebase (returns null from getConnector).  This can happen when connector instances for previously supported connector types remain in the table, or when switching back and forth between code versions which differ in their connector support.  Before these changes such connectors caused null pointer exceptions.  Now they are ignored.  In the case of such keys in the update worker task table, the task is also marked as DONE.
Minor rewording of google calendar reconnect required notification.