Added Several New Reference Events (#1500)

* added enum values for new events

* hooked up directory sync event

* upgraded the OrganizationUpgrade ReferenceEvent

* Added metadata to the OrganizationUserInvited event noting if this is the first event sent from an organization

* Added metadata to the AdjustedSeats event

* Implemented vaultImported event

* Implemented FirstGroupAdded event

* Implemented FirstCollectionAdded event

* Implemented FirstSecretAdded event type

* Implemented SalesAssisted reference event

* changed events to match updated requirements

* renamed an event enum

src/Core/Models/Business/ReferenceEvent.cs

@@ -42,7 +42,12 @@ namespace Bit.Core.Models.Business
 
         public PlanType? PlanType { get; set; }
 
+        public string OldPlanName { get; set; }
+
+        public PlanType? OldPlanType { get; set; }
+
         public int? Seats { get; set; }
+        public int? PreviousSeats { get; set; }
 
         public short? Storage { get; set; }