Bug 1069197 - added screen reader support for the calendar for the month...

... view.
we're slowly migrating the templates to ES6 quasi-literals (see Bug 1055432):

```js
day: function() {
  var date = this.h('date');
  var dateString = this.s('dateString');
  var id = this.s('id');
  var l10nState = this.l10nId('state');
  var state = this.s('state');

  return `<li role="gridcell" tabindex="0" id="${id}"
    aria-describedby="${id}-busy-indicator ${id}-description"
    data-date="${dateString}" class="${state}">
      <span class="day" role="button">${date}</span>
      <div id="${id}-busy-indicator" class="busy-indicator"
      aria-hidden="true"></div>
      <span id="${id}-description"
      aria-hidden="true" data-l10n-id="${l10nState}"></span>
    </li>`;
}
```