Add support for user high-contrast themes and dyslexia font

[ShGKme]

Issues:

• Add high-contrast theme
  • Add high contrast to the styles fetcher
  • Add app config setting to enable the styles
  • Add integration with the main process:
    • Also enable high contrast on the app level
    • Enable app config by default, if high contrast is enabled on the system
• Add dyslexia font
  • Add OpenDyslexic fonts from the server repo
  • Add styles from server's DyslexiaFont.php
  • Add a switch on the renderer process to enable the styles
    • For example, via a class/data attr on the body element
  • Add app config entry to enable the setting