Allow configuration of wifi credentials + hostname via settings.json

What it says on the tin.

• Replaces the hardcoded camp wifi credentials with ssid + psk read from settings.json. Also allows configuration of the badge network hostname.
• Adds barebones code for string type 'tunables'/settings. (Read only, can only be set via settings.json at the moment)
• Declaratively define hierarchical settings (sub-)menu structure
  • Only WiFi settings have their own submenu for now

Known issues: Display of string settings values in the settings screen is a bit glitchy. Not quite sure why, but I also haven't spent much time debugging it since this is just a barebones implementation for the functionality and the display issue is purely cosmetic and doesn't affect the core features of this patch.