Refactored all synchronizers to deal with some of the chronic issues.

Wino.Core.Domain/Entities/Shared/MailAccount.cs

@@ -106,6 +106,12 @@ public class MailAccount
     [Ignore]
     public MailAccountPreferences Preferences { get; set; }
 
+    /// <summary>
+    /// Last time folder structure was synchronized.
+    /// Used for optimization - skip folder sync if synced recently.
+    /// </summary>
+    public DateTime? LastFolderStructureSyncDate { get; set; }
+
     /// <summary>
     /// Gets whether the account can perform ProfileInformation sync type.
     /// </summary>