inbox: use pgp encryption (#70)

* inbox: use pgp encryption && other fixes
* fix inbox key last used at time
* remove inbox items if keys change or same item id syncs

* inbox:update inbox sync item
* rename item field to sync
* add alg field

* sync: delete inbox items after commit succeeds

* user: merge if conditions

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Co-authored-by: Abdullah Atta <abdullahatta@streetwriters.co>

Notesnook.API/Models/Algorithms.cs

@@ -22,6 +22,5 @@ namespace Notesnook.API.Models
     public class Algorithms
     {
         public static string Default => "xcha-argon2i13-7";
-        public static string XSAL_X25519_7 => "xsal-x25519-7";
     }
 }