Created and added content to Getting Started page

- How-to guide and gallery links have been disabled pending implementation. (have updated related jira issues)
- Created a ```disable-link``` CSS rule. 
- Introduced "API" and "How To Guide" badges (we may want to roll these out over the site)
- Updated "Getting Started" link on site, no longer points to GitHub
I've made an attempt at an explanation of the fact that charts can be created just using an object array and I think we could do with a how-to guide on the subject:

```html
<p>
    It is possible to use an object array directly as the data source for a chart. See the
    <a href="#" class="disabled-link">Simple charting <span class="badge">How To Guide</span></a> for more detail.
</p>

<p>
    However, in order to chart this data grouped by eye color, we will first need to create an
    <code>insight.DataSet</code> object.
    The data we use to initialise the data set should be an array of objects.
</p>
```