Closes#616
- Added small helper `NotificationSender` which is used to send
notifications.
- No notificaiton is sent on main thread.
- Change how `status` is stored and update in `SDKSynchronizer`. It is
now protected by lock. Before this wasn't needed because status was
updated from main thread everywhere.
- `SyncBlocksViewController` in the sample app now uses
`SDKSynchronizer` instead of `CompactBlockProcessor` directly.
Michal Fousek
Francisco Gindre