Add Settings with fullscreen and windowed options, a config file

(settings.toml) to persist settings, fix a bug in platform code where
innner window size wasn't updated on resize, various other tweaks

app/src/prelude.rs

@@ -11,6 +11,7 @@ pub use raidillon_platform::{
     Camera,
     PlatformContext,
     TimeContext,
+    settings::{Settings, WindowMode},
 };
 
 pub use raidillon_assets::{