Fixed: escape on a panel or popover breaks the key chain event

Previously when hitting escape on a CPPanel, the key chain event was broken.
Now when the user hit escape, cappuccino do the following process

- Check if the firstResponder or the chain of the nextResponder implement cancelOperation:
- If not, performKeyEquivalent on the firstResponder and so on
- If not, call the method cancel: on the firstResponder and the chain (not in the case of the CPPopover)

Previously, a complete: method was called if the user hit escape on a void window. This is not a feature of Cocoa, @aparajita  or @aljungberg can you confirm that ?

This commit is related to the commit #2139
This  is cocoa does.

This method is bound to the Escape and Command-. (period) keys. The key window first searches the view hierarchy for a view whose key equivalent is Escape or Command-., whichever was entered. If none of these views handles the key equivalent, the window sends a default action message of cancelOperation: to the first responder and from there the message travels up the responder chain.

If no responder in the responder chain implements cancelOperation:, the key window searches the view hierarchy for a view whose key equivalent is Escape (note that this may be redundant if the original key equivalent was Escape). If no such responder is found, then a cancel: action message is sent to the first responder in the responder chain that implements it.

NSResponder declares but does not implement this method.

https://developer.apple.com/library/mac/documentation/cocoa/reference/applicationkit/classes/NSResponder_Class/Reference/Reference.html#//apple_ref/occ/instm/NSResponder/cancelOperation: