[bug] Properly define stored window state (#638)

common/src/models/domain/windowState.ts

@@ -0,0 +1,10 @@
+export class WindowState {
+  width?: number;
+  height?: number;
+  isMaximized?: boolean;
+  // TODO: displayBounds is an Electron.Rectangle.
+  // We need to establish some kind of client-specific global state, similiar to the way we already extend a base Account.
+  displayBounds: any;
+  x?: number;
+  y?: number;
+}