Changed domains, configured links between VisaApplication and Applicant,created generic repository and repositories for domains

SchengenVisaApi/Domains/IEntity.cs

@@ -1,5 +1,8 @@
 namespace Domains
 {
     /// Interface that every entity should inherit from
-    public interface IEntity { }
+    public interface IEntity
+    {
+        public Guid Id { get; }
+    }
 }