Bug 1054178 - [Gaia][calendar] support 24 hour time format

I would probably move the ternary logic outside of the function call..

```js
format = _(format);
// we wrap the am/pm with JS because this keeps the locale file
// simpler and increases the flexibility.
// https://developer.mozilla.org/en-US/docs/Mozilla/Localization/Localization_best_practices#Avoid_unnecessary_complexity_in_strings
if (this.arg('addAmPmClass')) {
  format = format.replace(/\s*%p\s*/, '<span class="ampm">%p</span>');
}
var displayHour = localeFormat(date, format);
```
if your code can't fit into a single line, that is probably a sign that it should be split.