Added time tag with createdAt to tickets and retrospectives.

Adds 

```html
<time class="created-date ng-binding" itemprop="dateCreated" datetime="25/1/2014 18:38:14">25/1/2014 18:38:14</time>
```
to tickets and retrospectives

there is a lack of DRYness in this code, which is why I'm creating a PR instead of pushing it directly, in other words, I'd like some input on where to stick stuff like 'toLocaleStringSupportsLocales' so that it's DRY but still available in multiple controllers ( guess there's a angular way of doing this ).

For now I hardcoded it to locale : 'en-gb', I guess that works untill we start properly supporting localization. And when that happens we should really use the Accept-Languages header and handle this server-side, but that's a puzzle for another day.