Added the ability to define custom icons for the system tray. (#408)

* Added the ability to define custom icons for the system tray.

* Add placeholder icon if icon is not defined.

* Update themes

globals/systray.ts

@@ -0,0 +1,7 @@
+const systemtray = await Service.import('systemtray');
+
+globalThis.getSystrayItems = (): string => {
+    return systemtray.items.map((systrayItem) => systrayItem.id).join('\n');
+};
+
+export { getSystrayItems };