Add Snippets

@wallawe This adds snippets. The way it works now is you just enter the info in a form and if you go to `Snippets#show` you'll see the CSS/JS working. If you want to check it out, pull this down and create a Snippet in `rails console` with the following:

```
Snippet.create(title: "Sample", html: "<div>\r\n  <p class=\"test\">Hi there</p>\r\n</div>", css: "p.test {\r\n  background-color: blue;\r\n}", js: "alert(\"HI WILL!\");")
```