Added settings screen for push notification categories
Closes #45
Short description
Enables users to enable or disable specific categories of push notifications. Also makes it easier to add new settings panels in the future.
Steps to use this feature
- Open the 'Settings' section from the sidebar.
- Press 'Push Notifications'.
- Enable/disable categories as you please.
Note this feature requires concrexit!865 (closed) to function correctly. Without this fix, your push notification categories will all be enabled each time the app is freshly started.