My orders

Adds a tabbed section directive that allows defining a set of tabs that are used to select the section's template.
```html
<tabbed-section>
    <tab selected="true" tab-template="templates/template-path-1.html">Tab name 1</tab>
    <tab tab-template="templates/template-path-2.html">Tab name 2</tab>
    <tab tab-template="templates/template-path-3.html">Tab name 3</tab>
</tabbed-section>
```

Adds a tabbed section to the trading page that contains a table of the user's open offers.

Part of #765.

![screen shot 2014-09-10 at 7 42 41 pm](https://cloud.githubusercontent.com/assets/3108007/4228530/6f25510c-395d-11e4-9b01-ad011fc73ab7.png)