Move push notifications settings (regression from #5879) (#5941)

* Move push notifications settings

* fix typo `setf` -> `set`

app/javascript/mastodon/settings.js

@@ -0,0 +1,46 @@
+export default class Settings {
+
+  constructor(keyBase = null) {
+    this.keyBase = keyBase;
+  }
+
+  generateKey(id) {
+    return this.keyBase ? [this.keyBase, `id${id}`].join('.') : id;
+  }
+
+  set(id, data) {
+    const key = this.generateKey(id);
+    try {
+      const encodedData = JSON.stringify(data);
+      localStorage.setItem(key, encodedData);
+      return data;
+    } catch (e) {
+      return null;
+    }
+  }
+
+  get(id) {
+    const key = this.generateKey(id);
+    try {
+      const rawData = localStorage.getItem(key);
+      return JSON.parse(rawData);
+    } catch (e) {
+      return null;
+    }
+  }
+
+  remove(id) {
+    const data = this.get(id);
+    if (data) {
+      const key = this.generateKey(id);
+      try {
+        localStorage.removeItem(key);
+      } catch (e) {
+      }
+    }
+    return data;
+  }
+
+}
+
+export const pushNotificationsSetting = new Settings('mastodon_push_notification_data');