Core - Added ColorGradient type to use for.. gradients!

Core - Initialisation process no longer takes place in core constructor and is no longer async
UI - Fixed exceptions during init not being shown
Gradient editor - Started work on this

src/Artemis.UI/Screens/Splash/SplashViewModel.cs

@@ -47,22 +47,22 @@ namespace Artemis.UI.Screens.Splash
             base.OnClose();
         }
         
-        private void OnPluginServiceOnPluginLoaded(object? sender, PluginEventArgs args)
+        private void OnPluginServiceOnPluginLoaded(object sender, PluginEventArgs args)
         {
             Status = "Initializing UI";
         }
 
-        private void OnPluginServiceOnPluginLoading(object? sender, PluginEventArgs args)
+        private void OnPluginServiceOnPluginLoading(object sender, PluginEventArgs args)
         {
             Status = "Loading plugin: " + args.PluginInfo.Name;
         }
 
-        private void OnPluginServiceOnCopyingBuildInPlugins(object? sender, EventArgs args)
+        private void OnPluginServiceOnCopyingBuildInPlugins(object sender, EventArgs args)
         {
             Status = "Updating built-in plugins";
         }
 
-        private void OnCoreServiceOnInitialized(object? sender, EventArgs args)
+        private void OnCoreServiceOnInitialized(object sender, EventArgs args)
         {
             Execute.OnUIThread(() => RequestClose());
         }