WindowModule cannot be reopened after being closed

[DarthMazut]

Repro steps:

1. Get new instance of WindowModule
2. Open the window
3. Close the window
4. Try open it again

Actual: We are unable to reopen once closed window as _window.Content getter throws while trying to set its data context.

Expected: Client should be able to safely reopen once closed window.

But how to achieve it in such case?

• we could deceive the client and hide the window instead of closing it, but then again closing is something different than hiding...
• we could get new instance everytime clients wants to open a window, but this breaks registration process and we're loosing window state anyways