Update the demo to be compatible with more recent versions of WordPress, to add featured image support, fix bugs, and clean up the code.

* Set modal options later to dynamically set height based on the window.height
* Add featured image support
* Change namespace to gc_
* Fix javascript error with the river
* Increase size of the click target area in the modal
* Update design of the modal to work with jquery-ui 1.10 and to better match the design of WP
* Fix up the code formatting some
* Other bug fixes.