Image Modal CMS HTML Block subtype

- Added YAML file for the HTML template code for the modal to work
- Added CSS and JS code for modal to look and function properly
- Updated code to take comments into account.
- Simplified HTML template and expanded JS to set up image modal on load.
- Added preliminary drag script.
- Converted jQuery UI draggable to Draggabilly

@frrrances - here's the image modal branch! with Draggabilly and everything!

Here are some screenshots of how imageModal works. (This is using the Stanford theme, but would work equally well with the default courseware theme.)

When you first load an image modal it presents like this:
![screen shot 2014-01-30 at 9 43 56 am](https://f.cloud.github.com/assets/3364609/2042907/7021f6b8-89d7-11e3-98c7-99a03b69493a.png)

When you click on the image, it goes into the modal interface (starting in "fit to screen"):
![screen shot 2014-01-30 at 9 44 17 am](https://f.cloud.github.com/assets/3364609/2042923/a94d2188-89d7-11e3-82ec-350011599e0a.png)

Clicking the + magnifying glass makes the image full size and draggable (via draggabilly):
![screen shot 2014-01-30 at 9 44 28 am](https://f.cloud.github.com/assets/3364609/2042932/c63b06c0-89d7-11e3-918f-40b2c563b1cd.png)
![screen shot 2014-01-30 at 9 44 43 am](https://f.cloud.github.com/assets/3364609/2042935/cb154156-89d7-11e3-8c58-991af00f2a3f.png)

You can click the - magnifying glass to go back to the "fit to screen", or click the X to exit the modal.