IsTrackable/IsPersisted not updated after persisting an anchor

[finn-ellis]

Calling AnchorManager.CreateAnchor then persisting the new anchor with AnchorManager.PersistAnchor does not update either the Anchor.IsTrackable or Anchor.IsPersisted values when the Future completes.

See AnchorManager.PersistAnchor & AnchorManager.CompletePA

Fix: The anchor should have its properties updated when the internal Future is completed, or switched to getters.

[finn-ellis]

Fixed in pull request #24