Changes

• A bunch of internal rsRPC changes to make it better and more efficient
• Add INVITE_BROWSER support using rsRPC
  • This means that opening a server invite in the browser will automatically open it in Dorion now!
• Add more fine-grained configuration for the integrated RPC server
• Add full --os-accent CSS variable support for themes that use it
• Windows notifications now show the user's icon
• Add proxy configuration
  • This does not have a section in the UI, because if you require a proxy to access Discord, then you can't access the settings to begin with!
  • Instead, add your proxy server to Dorion's config.json manually.
• Fix some fullscreen behaviour
• Fix showing window on macOS (#267)