Feature sync on refresh (#937)

* Added new option: Sync on refresh

* Removed unused field

* Fixed refreshing on disappearing & unnecessary codes removed

* Requested changes

* Calling storage service instead of a dedicated service function (mobile-specific)

src/Core/Abstractions/ISyncService.cs

@@ -7,7 +7,6 @@ namespace Bit.Core.Abstractions
     public interface ISyncService
     {
         bool SyncInProgress { get; set; }
-
         Task<bool> FullSyncAsync(bool forceSync, bool allowThrowOnError = false);
         Task<DateTime?> GetLastSyncAsync();
         Task SetLastSyncAsync(DateTime date);