Import list of Git screencasts from gitcasts.com

As part of consolidation efforts, this brings in the gitcasts.com
page which listed the screencasts posted at youtube.com/github

By default it embeds the first lesson onto the page.

If the user wants to know more they can find out via the links
to the other episodes in the series.

To keep from touching more HTML templates, the page generation
has been thrown into the `rake` process, sloppily cribbed from
the regular page generation method.
Load and watch screencasts without leaving page

Adds a dirty amount of JavaScript and jQuery to catch the link
of the desired screencast and then swap out the embedded
YouTube video link. Also scrolls the page up in case you've
clicked an item that pushed the video out of full view.

If JavaScript is disabled on client-side this will still
allow the user to click through and view the video on YouTube.
Merge pull request #33 from randomecho/gitcasts

Import list of Git screencasts from gitcasts.com