Cocoa: Clear window hash entry in ~QCocoaWindow.

The Cocoa platform plugin maintains a NSWindow->
QCocoaWindow hash.

Hash entries was not properly cleared on QCocoaWindow
destruction. Add call to clear the entry for the
destroyed window. Make QCocoaIntegration remove
the key from the hash in this case instead of
setting it to 0.

Task-number: QTBUG-37597
Change-Id: I3adaeee45069aea1d2ecacd948298302eafe1929
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Update Copyright year in commercial nag screens

Change-Id: I70420c44c018dbe733a50badb7f9f7f419459f7a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>