Revert "don't allow views from another window to be next/previouskeyViews"

This reverts commit 7fab8d9782d4604c4441e48701f9207e4a2b4229.

This breaks the repsonder chain if it is defined in a view that has no window yet.
Details and reduction here: https://github.com/cappuccino/cappuccino/commit/7fab8d9782d4604c4441e48701f9207e4a2b4229#commitcomment-2781849