refactor(ISignature): create to handle common properties of a signature

- implement to entity and dto

EnvelopeGenerator.Domain/Entities/Signature.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel;
+using EnvelopeGenerator.Domain.Interfaces;
+using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 using System.ComponentModel.DataAnnotations.Schema;
 #if NETFRAMEWORK
@@ -13,7 +14,7 @@ namespace EnvelopeGenerator.Domain.Entities
 #endif
 
 [Table("TBSIG_DOCUMENT_RECEIVER_ELEMENT", Schema = "dbo")]
-public class Signature
+public class Signature : ISignature
 {
     public Signature()
     {

EnvelopeGenerator.Domain/Interfaces/ISignature.cs

@@ -0,0 +1,11 @@
+namespace EnvelopeGenerator.Domain.Interfaces
+{
+    public interface ISignature
+    {
+        int Page { get; set; }
+
+        double X { get; set; }
+
+        double Y { get; set; }
+    }
+}