Add ability to navigate serach results with keyboard

This allows you to:

- navigate up and down the list of results with UP/DOWN, or TAB / SHIFT+TAB
- add the selected class by pressing the ENTER key
- clear search with the ESC key
- clear search by clicking outside the search results
- continue to use the mouse as expected, including adding classes and clicking into the search box to edit queries

Selected result (which will be added if ENTER is clicked) is shown in blue, and defaults to the first element.  Elements also turn gray on hover, and can be clicked to be added.  (this mirrors the Google Chrome omnibar search behavior)

![screen shot 2014-07-31 at 1 31 20 am](https://cloud.githubusercontent.com/assets/2433509/3760269/f01dc10a-1873-11e4-9711-9ef0419d430b.png)
This block of code is kinda sketchy.  Because `Deps.autorun` will run after the `results` exist but before the DOM elements do, I have to do setInterval magic to wait for the DOM to exist in order to select the first result.

The solution to this would be adding a `selected` class to the first element in the templating, but you can't get the loop index or figure out which one is first when using `#each`.

The only way to get around it in my mind is to give them all `selected`, and use css like:

```less
courseResultItem.selected {
  background-color: @blue;
  
  &+.selected {
    background-color: @white;
  }
}
```

which would make it so that only elements that are selected and not preceeded by an element that is selected will actually have the `@blue` background.  We would then need to change the ENTER key handler to reflect this:

```
$('.courseResultItem.selected:not(.selected+.selected)').click();
```