Add warning on device card for outdated devices.

Server/Components/Devices/DeviceCard.razor

@@ -10,9 +10,21 @@
 
     <div class="card-header">
         <div>
-
-            <i class="oi oi-power-standby @(Device.IsOnline ? "text-success" : "text-danger")"
-               title="@(Device.IsOnline ? "Online" : "Offline")"></i>
+            @if (Device.IsOnline)
+            {
+                if (IsOutdated)
+                {
+                    <i class="oi oi-power-standby text-warning" title="Agent Outdated"></i>
+                }
+                else
+                {
+                    <i class="oi oi-power-standby text-success" title="Online"></i>
+                }
+            }
+            else
+            {
+                <i class="oi oi-power-standby text-danger" title="Offline"></i>
+            }
         </div>
         <div class="overflow-hidden ml-2">
             <div class="d-inline-block">

Server/Components/Devices/DeviceCard.razor.cs

@@ -52,6 +52,10 @@ namespace Remotely.Server.Components.Devices
 
         private bool IsSelected => AppState.DevicesFrameSelectedDevices.Contains(Device.ID);
 
+        private bool IsOutdated =>
+            Version.TryParse(Device.AgentVersion, out var result) && 
+            result < ParentFrame.HighestVersion;
+
         [Inject]
         private IJsInterop JsInterop { get; set; }
 

Server/Components/Devices/DevicesFrame.razor.cs

@@ -42,6 +42,8 @@ namespace Remotely.Server.Components.Devices
         private string _selectedSortProperty = "DeviceName";
         private ListSortDirection _sortDirection;
 
+        public Version HighestVersion { get; private set; }
+
         [Inject]
         private IClientAppState AppState { get; set; }
 
@@ -222,6 +224,8 @@ namespace Remotely.Server.Components.Devices
 
             _allDevices.AddRange(devices);
 
+            HighestVersion = _allDevices.Max(x => Version.TryParse(x.AgentVersion, out var result) ? result : default);
+
             FilterDevices();
         }