Move window centering to utils

ext/src/lib/utils.js

@@ -8,3 +8,14 @@ export function getNextEllipsis (ellipsis) {
         else if (ellipsis === "...") "";
     };
 }
+
+export function getWindowCenteredProps (refWin, width, height) {
+    const centerX = refWin.left + (refWin.width / 2);
+    const centerY = refWin.top + (refWin.height / 3);
+
+    return {
+        width, height
+      , left: Math.floor(centerX - width / 2)
+      , top: Math.floor(centerY - height / 2)
+    };
+}