Renders latest activity update date

Yavsc/ApiControllers/GCMController.cs

@@ -56,6 +56,16 @@ public class GCMController : Controller
                 _context.GCMDevices.Add(declaration);
                 _context.SaveChanges();
             }
+            if (declaration.LatestActivityUpdate > default(DateTime))
+            {
+                var latestActivityUpdate = _context.Activities.Aggregate(
+                    (a,b)=>a.DateModified>b.DateModified?a:b
+                ).DateModified;
+                return Json(new { 
+                    IsAnUpdate = deviceAlreadyRegistered, 
+                    UpdateActivities = latestActivityUpdate>declaration.LatestActivityUpdate?true:false 
+                    });
+            }
             return Json(new { IsAnUpdate = deviceAlreadyRegistered });
         }
         return new BadRequestObjectResult(ModelState);