Escape key closes windows

The default behaviour of a TraitsUI window is that the escape key closes the window with the same behaviour as clicking the close titlebar icon. This is probably OK for modal dialogs, but is not good behaviour for things which are intended to be more long-lived (eg. project or document style windows).

Currently this is fairly hard-coded behaviour; there are no view-level options to turn it on or off. It can be worked around with a "do nothing" keybinding for the escape key, but the fix is not obvious and may have other side-effects.

Probably the best behaviour would be to remove the current hard-coded behaviour, and add default keybindings for escape that replicate the existing behaviour. Users would then be able to override using a different set of keybindings.