Bug 1070895 - Pressing ENTER in search box clears search and returns back to inbox

* Makes sure a 'submit' listener is in place to stop accidental form submissions (usually by the Enter button on keyboard) from trying to submit the form. This will give us protection if the building block moves away from type="submit" or some other submit pathway shows up later.
* For the click handler for Cancel, make sure it is a real Cancel click and not a simulated one from a submit action.
* Turn off autocorrect for the search input. Now that the Enter button does not destroy the card, the text being autocorrected by the keyboard on Enter.
I think we should set "inputmode" as well as x-inputmode.