Added the store for dynamically changing the popup titles

src/stores/popup.ts

@@ -0,0 +1,15 @@
+import { derived, writable } from "svelte/store";
+import { PLUGIN_NAME } from "$lib/constants";
+
+/**
+ * Store containing the name of the subpage. This name will be added to the title alongside the name of the plugin.
+ */
+export const popupTitle = writable<string | null>(null);
+
+/**
+ * Name of the current route with the name of the plugin appended to it.
+ */
+export const headTitle = derived(
+  popupTitle,
+  $popupTitle => ($popupTitle ? `${$popupTitle} | ` : '') + PLUGIN_NAME
+);