Desktop settings

[ShGKme]

• [ ] Add backend API for storing, reading and updating application-level settings
• [ ] Add IPC API to use settings in the frontend
• [x] Add Talk Frontend API to add new Talk settings sections
• [ ] Add components and modules to work with settings on the Talk Desktop frontend

Follow-up:

• [ ] Implement settings:
  • [ ] General:
    • [ ] Run on startup
  • [ ] Appearance:
    • [ ] Theme
    • [ ] Use custom title
    • [ ] Spellcheck languages
  • [ ] Notifications:
    • [ ] Enable notifications
    • [ ] Play custom Talk notification sounds or system notification sound
  • [ ] Privacy:
    • [ ] Show/hide message content in a notification
    • [ ] Show/hide message author in a notification