Make Orders IObservableCollection and add a ReloadOrders method.

- IObservableCollection emits a CollectionChanged event.
- We handle this event in classes that need to it changed.
- ReloadOrders refreshes the collection from the Database.
Handle the repositories Orders.CollectionChanged method.

- if the repository collection changes,
- then we update the user interface.
Pass the repository to the SyncCommandsViewModel, because we want to update the repository after sync.