[esc] key cancels editing mode (without saving)

[nelsonic]

According to: https://github.com/tastejs/todomvc/blob/master/app-spec.md#editing

If escape is pressed during the edit, the edit state should be left and any changes be discarded.

and the test assertions: https://github.com/tastejs/todomvc/tree/master/tests#example-output

✓ should cancel edits on escape (1115ms)

• [x] Add keyboard event listener case in subscriptions for [esc] key
• [x] Trigger signal('CANCEL')() to cancel editing without saving changes.

[nelsonic]