fix(md-calendar): boundKeyHandler preventDefault on other input elements

[NgaiKaKit]

If use the md-calendar directly in the body without datepicker, boundKeyHandler will disable some keyEvent on other input elements in the page. So only apply the handleKeyEvent on the document.body when the md-calendar is inside datepicker. Otherwise, apply on the calendar element only.

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[crisbeto]

Thank you for the PR. I actually did something similar in #9641, although it shouldn't hurt fixing it until #9641 is merged. Your tests seem to be failing, because they're still dispatching key events to the body, instead of the element. See https://github.com/angular/material/blob/master/src/components/datepicker/js/calendar.spec.js#L116

[crisbeto]

It might be a little more readable if you defined the handleKeyEvent in an else block. Also you can refer to this.$element as just $element:

if ($element.parent().hasClass('md-datepicker-calendar')) {
  handleKeyElement = angular.element(document.body);
} else {
  handleKeyElement = $element;
}

[crisbeto]

You don't need this check. The calendar here will always be on it's own (without the datepicker).

[crisbeto]

LGTM @ThomasBurleson. @NgaiKaKit could you try signing the CLA again? Otherwise the PR can't be merged.

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