#326: fast Ctrl[+Shift]+Tab will not be ignored

Quickly pressing Ctrl+Tab/Ctrl+Shift+Tab is often ignored.

This is happening because KeyDown is used to turn on navigator window and KeyUp is used to both intercept keys and turn navigator window off. When Ctrl+Tab pressed quickly KeyDown turn navigator window on, but there is no KeyUp for Ctrl+Tab (it's just Tab).

Proposed fix use PreviewKeyDown to activate and intercept navigator window keys; PreviewKeyUp to deactivate navigator window.