Add SwitcherControls component

## Overview
This PR adds a component for showing a countdown to the next dashboard. The countdown element itself is clickable so that one may switch to the next dashboard immediately. Each element and sub-element has their own ID attribute so that users can control styling as they like, prefaced with `dc-switcher-` for namespace consistency.

## Use
The only requirement to use this component is to define an element with an id of `dc-switcher-controls`.

# Example
![switcher-countdown](https://cloud.githubusercontent.com/assets/7836/5530706/00aad53c-89f1-11e4-8724-faa46a00acf8.png)

```html
    ...

    <style>
    #dc-switcher-arrow { font-size: 22px; }
    #dc-switcher-controls:hover { cursor: pointer; cursor: hand;}
    </style>

    ...

    <div style='color: white;'>
      <div id='dc-switcher-controls' style='float: right; margin-right: 10px'>
      </div>
      <div style='clear: both'>
      </div>
    </div>

    ...

    <!-- automatically switch dashboards every 60 seconds -->
    <div id="container" data-switcher-interval="60000" data-switcher-dashboards="apis pivotal">
      <%= yield %>
    </div>
```