Topic/1529 handle external user invitation

coscine/issues#1529

src/Project/Controllers/ProjectController.cs

@@ -665,7 +665,7 @@ namespace Coscine.Api.Project.Controllers
                 {
                     ["placeholder"] = new JObject()
                     {
-                        ["confirmation_link"] = $@"{_configuration.GetString("coscine/local/api/additional/url")}/invitation?token={token}"
+                        ["confirmation_link"] = $@"{_configuration.GetString("coscine/local/api/additional/url")}/SitePages/Home.aspx?token={token}"
                     }
                 }
             };
@@ -757,7 +757,7 @@ namespace Coscine.Api.Project.Controllers
 
             _invitationModel.Delete(invitation);
 
-            return Ok($"User {user.Id} is now {role.DisplayName} of project {project.Id}.");
+            return NoContent();
         }
 
         private static bool IsValidEmail(string email)