Added theming support. Added import/export

Missing: API Server save

Moonlight.Client/Services/ThemeService.cs

@@ -0,0 +1,25 @@
+using MoonCore.Attributes;
+using Moonlight.Shared.Misc;
+
+namespace Moonlight.Client.Services;
+
+[Singleton]
+public class ThemeService
+{
+    public event Func<Task> OnRefresh;
+    
+    public Dictionary<string, string> Variables { get; private set; } = new();
+    
+    public ThemeService(FrontendConfiguration configuration)
+    {
+        // Load theme variables into the cache
+        foreach (var themeVariable in configuration.Theme.Variables)
+            Variables[themeVariable.Key] = themeVariable.Value;
+    }
+
+    public async Task Refresh()
+    {
+        if (OnRefresh != null)
+            await OnRefresh.Invoke();
+    }
+}