Notification problems on release-5.9, 5.10 and 5.11

Notifications have been a problem in Fork. Here are the major issues:

1. Badge count missing / not reflecting correct numbers / not updating at background (problem addressed in #74.

Temporary Solution: Ask the users to terminate other Telegram session in the same iOS device & reboot.

2. No banner alert even if all notification types (Alerts in Lock Screen, Notification Center, Banners, Banner Style: Temporary, Sound & Badge enabled) are enabled in iOS Settings > Notifications.

For problem 2, I still don't figure out a solution yet. In TelegramUI's AppDelegate.swift line 1858, it registers all types of notifications by default. Anyone can share some lights?

What is the difference between Fork and official app regarding notifications? do the Telegram servers marked Fork clients having lower priority to receive notifications / updates?

3. Background update task used too much battery (problem addressed in #81), and solved in release-5.9.

Start with TelegramUI's AppDelegate.swift around line 1858, where notification types are registered, and investigate the missing banner alert described in problem 2. Compare Fork's notification behavior with the official app and reproduce the issue with the listed iOS notification settings enabled. Done means banner alerts appear reliably under those settings; problems 1 and 3 are already addressed in #74 and #81.