Plugins - Added platform support

Settings - Fixed updating issues in plugin tab
UI - Don't initialize in design mode
UI - Move ReactiveCoreWindow to Artemis.Shared
Window service - Return window created by ShowWindow
Window service - Added CreateOpenFileDialog API

src/Artemis.Core/Plugins/PluginFeatureAttribute.cs

@@ -26,6 +26,7 @@ namespace Artemis.Core
 
         /// <summary>
         ///     Marks the feature to always be enabled as long as the plugin is enabled
+        ///     <para>Note: always <see langword="true"/> if this is the plugin's only feature</para>
         /// </summary>
         public bool AlwaysEnabled { get; set; }
     }

src/Artemis.Core/Plugins/PluginFeatureInfo.cs

@@ -122,10 +122,11 @@ namespace Artemis.Core
         }
 
         /// <summary>
-        ///     Marks the feature to always be enabled as long as the plugin is enabled and cannot be disabled
+        ///     Marks the feature to always be enabled as long as the plugin is enabled and cannot be disabled.
+        ///     <para>Note: always <see langword="true"/> if this is the plugin's only feature</para>
         /// </summary>
         [JsonProperty]
-        public bool AlwaysEnabled { get; }
+        public bool AlwaysEnabled { get; internal set; }
 
         /// <summary>
         ///     Gets a boolean indicating whether the feature is enabled in persistent storage

src/Artemis.Core/Plugins/PluginInfo.cs

@@ -24,7 +24,7 @@ namespace Artemis.Core
         private Plugin _plugin = null!;
         private Version _version = null!;
         private bool _requiresAdmin;
-
+        private PluginPlatform? _platforms;
 
         internal PluginInfo()
         {
@@ -142,7 +142,17 @@ namespace Artemis.Core
             get => _requiresAdmin;
             internal set => SetAndNotify(ref _requiresAdmin, value);
         }
-        
+
+        /// <summary>
+        /// Gets 
+        /// </summary>
+        [JsonProperty]
+        public PluginPlatform? Platforms
+        {
+            get => _platforms;
+            internal set => _platforms = value;
+        }
+
         /// <summary>
         ///     Gets the plugin this info is associated with
         /// </summary>
@@ -164,6 +174,11 @@ namespace Artemis.Core
                 return Icon.Contains('.') ? Plugin.ResolveRelativePath(Icon) : Icon;
             }
         }
+        
+        /// <summary>
+        /// Gets a boolean indicating whether this plugin is compatible with the current operating system
+        /// </summary>
+        public bool IsCompatible => Platforms.MatchesCurrentOperatingSystem();
 
         internal string PreferredPluginDirectory => $"{Main.Split(".dll")[0].Replace("/", "").Replace("\\", "")}-{Guid.ToString().Substring(0, 8)}";
 

src/Artemis.Core/Plugins/PluginPlatform.cs

@@ -1,4 +1,5 @@
 using System;
+using Newtonsoft.Json;
 
 namespace Artemis.Core;
 
@@ -6,15 +7,36 @@ namespace Artemis.Core;
 ///     Specifies OS platforms a plugin may support.
 /// </summary>
 [Flags]
+[JsonConverter(typeof(Newtonsoft.Json.Converters.StringEnumConverter))]
 public enum PluginPlatform
 {
     /// <summary>The Windows platform.</summary>
-    Windows = 0,
+    Windows = 1,
 
     /// <summary>The Linux platform.</summary>
-    Linux = 1,
+    Linux = 2,
 
     /// <summary>The OSX platform.</summary>
     // ReSharper disable once InconsistentNaming
-    OSX = 2
+    OSX = 4
+}
+
+internal static class PluginPlatformExtensions
+{
+    /// <summary>
+    ///     Determines whether the provided platform matches the current operating system.
+    /// </summary>
+    internal static bool MatchesCurrentOperatingSystem(this PluginPlatform? platform)
+    {
+        if (platform == null)
+            return true;
+
+        if (OperatingSystem.IsWindows())
+            return platform.Value.HasFlag(PluginPlatform.Windows);
+        if (OperatingSystem.IsLinux())
+            return platform.Value.HasFlag(PluginPlatform.Linux);
+        if (OperatingSystem.IsMacOS())
+            return platform.Value.HasFlag(PluginPlatform.OSX);
+        return false;
+    }
 }

src/Artemis.Core/Plugins/Prerequisites/PluginPrerequisite.cs

@@ -101,16 +101,7 @@ namespace Artemis.Core
         /// </summary>
         public bool AppliesToPlatform()
         {
-            if (Platform == null)
-                return true;
-
-            if (OperatingSystem.IsWindows())
-                return Platform.Value.HasFlag(PluginPlatform.Windows);
-            if (OperatingSystem.IsLinux())
-                return Platform.Value.HasFlag(PluginPlatform.Linux);
-            if (OperatingSystem.IsMacOS())
-                return Platform.Value.HasFlag(PluginPlatform.OSX);
-            return false;
+            return Platform.MatchesCurrentOperatingSystem();
         }
 
         /// <summary>