feat(config): add active window border style opt

This commit adds a new active window border style configuration option
to komorebi.json, allowing users to explicitly opt in to square or
rounded active window borders to match whatever patches they may have
made at the system / dwm.exe level.

komorebi/src/lib.rs

@@ -194,6 +194,9 @@ lazy_static! {
         )
     };
 
+    static ref ACTIVE_WINDOW_BORDER_STYLE: Arc<Mutex<ActiveWindowBorderStyle>> =
+        Arc::new(Mutex::new(ActiveWindowBorderStyle::System));
+
     static ref BORDER_RECT: Arc<Mutex<Rect>> =
         Arc::new(Mutex::new(Rect::default()));