[WISH] Close dialogs with ESC key

[gh658804]

It would be nice if all dialogs could be closed when pressing the ESC key.

[mimecorg]

The problem is that in some dialogs you can enter large amount of information, for example issue description or comment, and it would be easy to lose it by pressing ESC key accidentally. That's why at the moment only windows that don't have the OK/Cancel buttons can be closed using the ESC key.

A better solution would be probably to display a confirmation message when some text is entered and ESC or Cancel is pressed, but I'm leaving it for a future release.