Upgrade notifee dependency to latest and refactor

[lyqht]

Following the issue created on Notifee, a fix has been implemented.

Tasks:

• Upgrade to latest dependency ^5.2.1 and test that notification still works as intended
• Refactor the code to the initial implementation as mentioned in the issue, for cleaner code.

To verify that the notification works as intended:

• Create a bill with a notification
• See the notification showing up on mobile without error